So, as the rumors are pouring in about Roboute Guilliman (the first member of the latest Triumvirate that we have solid rules on), it looks like he has the following profile:
WS9 BS6 S6 T6 W6 I6 A6 Ld10 Sv 2+/3++ (Monstrous Creature, Character) — (70 MBs cost)
-Preferred Enemy (Forces of Chaos)
-Chapter Tactics (Ultramarines)
-Unyielding Will — His Leadership can never be impacted by negative modifiers
-Lord Commander of the Imperium — All friendly Imperium units in his army re-roll all failed Morale/Fear/Pinning checks.
-Primarch of the XIII Legion — Gives all Ultramarines in his army access to an additional use of Tactical, Assault, AND Devastator Doctrines
-Absolute Mastery — Has all six Command Traits (i.e. all friendly units within 12″ use his Ld, have Move Through Cover, gain +1″ to Run and Charge moves, re-roll 1s to Hit in both Shooting and Assault, and all enemy units within 12″ use their lowest Ld).
-Armor of Fate — Gives him 2+/3++ and each time he dies, on a roll of 4+, he comes back to life next turn with D3 wounds.
-Emperor’s Sword and Hand of Dominion — As a shooting weapon, gives, 24″ S6 AP2 Assault 3 Rending weapon and in close combat gives him a S10 AP1 Armourbane, Concussive, Soul Blaze weapon that strikes at full I6. Additionally, any rolls to Hit of 6 become Destroyer attacks (so great for killing ICs, vehicles, and other LOWs) and he can choose to swap all his normal attacks for a single “sweep” attack which automatically hits all enemy models within 1″ of him (so great for single-handedly clearing out hordes).
Looking at all this and considering that he only costs 70 MBs and a LOW slot, in many ways Guilliman is an exceptional bargain, especially considering all the buffs he gives out and how ridiculously hard he hits in close combat. He really can take all comers in the Assault Phase, with the ability to deal with everything from Greater Daemons and GMCs like Wraithknights to tar-pitting masses of Gaunts, Cultists, Ork Boyz, Hybrid Acolytes etc.
In terms of being a force multiplier to his army, with any Imperium faction (which is pretty much any army that you would play him with, since everyone else is Allies of Convenience, i.e. Eldar/Harlequins, or worse, i.e all the other factions), then you can easily make hims the “flagship” of either a shooty gunline or the anchor of an advancing foot-slogging assault force (i.e. Black Templars, Skitarii, foot Sisters of Battle, etc.). Then your opponent is forced to make a decision.. try and kill Guilliman to “de-force multiple” (which will take a significant portion of his combat power to do), or try and kill the rest of the allied forces while Guilliman continues to buff them and move himself closer to getting into melee with your forces… either way, it is a tough choice and, given that the Ultramarine Primarch is such a bargain points cost for all his abilities, you can still have a substantial army around him.
Weighed against this are two major negatives: first, as a Monstrous Creature, there is not way for him to join squads, be joined, or use Look Out Sir! (we will see if future formations or 8th edition changes this, but for now this it how it stands), meaning that he is basically as tough as a Riptide with an extra wound, Stimulant Injectors, and Nova Reactor shielding activated… on other words, tough, but very kill-able, especially to massed Grav, Eldar D-Weapons, and/or Poison, which are all quite common in competitive games (especially Grav). While he does have EW and so cannot be “one-shotted” by Instant Death weapons like other MCs can be, if you opponent can concentrated fire it only takes an average of 40 x BS4 Grav Cannon/Amp shots to bring him down. That, or lucky D weapon shots, will be a difficult threat to deal with for any armies fielding Guilliman, especially if these weapons can Alpha Strike via Drop Pod, Deep Strike, etc.
The second major issue is that, as a non-Flying/Jump MC, he cannot get in vehicles and must foot-slog forward at 6″ a turn, which greatly limits his mobility (also durability, since he can’t use transports to protect him from enemy shooting) and makes it difficult to catch enemy forces in close combat and use his amazing abilities in that arena. If your plan is to just use him as an assault “smasher,” then I think you will have significant trouble getting the most out of him, since a savvy opponent will simply kite away, use sacrificial screening units, and/or shoot him down before he can actually come to grips with his target(s) in assault. Additionally, this creates a problem for trying to keep in “buffing range” for any fast moving armies (i.e. Bikers, Mechanized units, Deep Striking forces, etc.), since Guilliman can only move 6″ and run a maximum of 7″ additional each turn (having Fleet does help a little here, but of course he has to sacrifice shooting to use it and still hope his Run rolls are good).
So, considering all that, is Roboute Guilliman worth investing in for a competitive army? I think the answer is “Yes,” but you can’t just throw him blindly out there and expect to excel. First, you have to craft an army that maximizes his strengths and force-multiplying skills… obviously, Ultramarines automatically get the most of any faction in having him on the board, since they are guaranteed two Devastator, two Assault, and two Tactical doctrines usages per game. While I think many different builds can actually make good use of him, probably one of the strongest is an advancing “gunline” style army that puts out tons of firepower and slowly, relentlessly moves toward your opponent (kind of like an Imperium version of Necrons 😉 ). In this way, Guilliman can maximize the buffs he puts out, keep up with the army, and serve as a ridiculously powerful “counter-assault” element if your opponent tries to get in close to your forces (remember, with Fleet and +1″ to his Charge ranges, he has something like a 10″ average charge distance).
Secondly, I think you have to actively work to mitigate his weaknesses in mobility and his vulnerability to certain kinds of enemy shooting… here are some ideas that might help in this area:
 Void Shield Generator — If you are planning to have him sit back and buff/protect your fire base, then a Void Shield Generator can give him in essence 3 x AV12 “layers” that your enemy has to deal with before targeting Guilliman… this is especially key against Grav weapons and can really make the difference between him surviving as Alpha Strike by units with them or not.
 Heavy Cover and “The Shrouding” psychic power — While he naturally has a 2+/3++, even that 3++ fails a 33% of the time against AP2/1 weaponry (again, Grav is one of the biggest culprits here). By combining Heavy Cover (4++ cover save) and Shrouding you give him a 2++ cover save, which reduces wounds inflicted by AP2/1 weapons by 16% compared to his normal wargear… not enough to make him invincible, but enough to help him survive long enough so that you can eliminate the key threats to him before your opponent gets another Shooting Phase.
 “Earth Blood” and “Endurance” psychic powers — Earth Blood restores D3 wounds and gives him IWND, so if you are lucky you can bring back a maximum of 4 lost wounds in a single turn, which would go a long way to helping him survive the entire game. Endurance improves his FNP from a 5+ to a 4+, which isn’t major, but like the discussion with Shrouding above, it reduces overall damage to him by an average of 16%, which in a game of small margins, can be the difference between victory and disaster for Guilliman specifically and your army as a whole.
 “Electrodisplacement” psychic power — Considered one of the most OP/imbalanced powers in the game right, nevertheless it can make a big difference for getting Guilliman into combat. Drop Pod a Librarian with this power next to a enemy target unit Turn 1, then cast the power to “switch” places between Guilliman and the Librarian, then charge that target enemy unit with Roboute in the Assault Phase of that same turn… if successful, you can have him tearing up enemy forces in close combat from right out the gate, not to mention the massive Psychological blow to your opponent when he finds his Stormsurge or Wraithknight or Hive Tyrant or Grav Centurions locked in combat with a Primarch before it ever even gets to move/shoot.
 “Magnetokinesis” psychic power — While Guilliman cannot charge after using this ability, if cast successfully it does allow him to move another 18″ without needing to run (so a net of 24″ in one turn), which makes him more than able to keep up with fast-moving allied units and also immediately puts the pressure on your opponent as you threaten a Turn 2 charge with a potent MC in his phase (NOTE: This tactic can work especially well, I think, if used in conjunction with multiple Shunting Dreadknights, putting a “threat overload” of deadly Imperial Monstrous Creatures in his face right away, making it difficult to choose what to deal with and really putting him on the horns of a dilemma).
 “Invisibility” psychic power — This is the gold standard of powers to enhance Guilliman, I think. If you can get it off successfully on him, then he is completely immune to any Blasts or Templates, which is what most D weapons are (unless they have a lucky scatter onto him) and even against massed Grav he becomes SO much more survivable. With Invisibility successfully cast, it takes an average of 27 Grav Cannon/Amp shots to cause a single Unsaved Wound to Guilliman (without Invisibility, it takes an average of 7 Grav Cannon/Amp shots to cause a single Unsaved Wound), so about 160 Grav shots to actually kill him. If you can get this off, then Guilliman is basically invulnerable and all you have to worry about is his mobility issues and maximizing his positioning to buff the rest of your army.
 Lias Issodon and Infiltration — If you are willing to give up the tremendous benefits of his powerful Warlord Traits (and they are pretty major), you can take Lias Issodon as your Warlord and use his Master of Ambush WL Trait to Infiltrate Guilliman 18″ away from enemy forces, which gives him a greatly enhanced chance of moving in and, by Turn 2, catching enemy units in close combat (i.e. move 6″ and then run an average of another 5″, putting him 7″ away from your opponent by the end of the turn). While there is a big trade-off with this tactic, it can be quite effective for maximizing his potent close combat skills.
Besides all that I have mentioned already, one additional thing to note is, given how powerful Guilliman is and what a threat he can be, another role he can play is that of “fire magnet” for the rest of your army by drawing away firepower that would otherwise be a real threat to the units around him. Outside of Grav, D Weapons, and exceptionally massed poison, he can really “tank” quite a lot of damage, as it takes the following to inflict a SINGLE unsaved wound on him:
[a] BS4 Bolter — 81 shots
[b] BS4 Scatter Laser — 27 shots
[c] BS3 TLed High Yield Missile Pod — 18 shots
[d] BS4 Plasma Gun — 10 shots
[e] BS4 Lascannon/Bright Lance/Dark Lance/Railgun– 8 shots
[f] BS4 Splinter Rifle/Cannon — 27 shots
All of this is for a single wound, so it takes 6 times this to kill him on average (and then he has a 50% chance of coming back to life), so played right you can really use him to effectively absorb combat power away from the rest of your army list.
Overall, I am pretty excited to see Guilliman get rules for 40K and will very interested to see how his performance holds up in competitive play… as I said at the beginning here, with savvy employment, I think he can be a great addition to any Imperium army, ESPECIALLY an Ultramarine one (I myself currently run a partial Ultramarine Army right now)!