Space Marine Relics haven’t changed that much from the previous codex, but they are still quite viable and, in general, worth their points cost. Let’s take a look:
1 – The Primarch’s Wrath — This may very well be the Relic with the best “value” in the codex. For only the cost of 4 MBs, you get a S4 AP4 weapon with Salvo 3/5, Shred, and Master-crafted rules. Take on a Captain, Chapter Master, or Techmarine (all of these have BS5) and supported by Relentless from riding a Bike or wearing Terminator Armor, this shooting Relic is outstanding against anything with a 4+ save or worse. Between BS5 and Master-crafted, you are likely to get 5 hits and, shooting against T3 foes like AM Veterans, Eldar Aspect Warriors, Tyranid Gaunts, or Tau Fire Warriors, the combination of S4 and Shred means you are likely to inflict 4-5 wounds, all with AP4. Put another way, your SM character equipped with The Primarch’s Wrath can reliably kill half a squad of these kind of warrior’s each shooting phase, more than making back its points many times over during the course of a normal game. Even against MEQs, the high volume of fire and Shred USR means that this Relic can knock down a model or two each shooting phase.
2 – Teeth of Terra — This is basically a Relic Blade that costs an extra 2 MBs, but also grants the user Rampage, and Concussive for its Melee attacks. That is quite a bargan, especially if the bearer is employed in a way that he is likely to be outnumbered (the 1-3 extra attacks alone are worth the points increase). i think this Relic works best when paired with a Power Fist or Thunder Hammer… since the Teeth of Terra is a Specialist Weapon, when a character has both it and a PF/TH, he gets +1A for fighting with two weapons and has the option, if up against a high Toughness opponent, vehicle, and/or enemy with a 2+ save, to switch to the PF/TH for S8 AP2 Unwieldy attacks. Overall, I think the Teeth of Terra is another very good value Relic, especially when used with another Specialist Weapon and taken for a dedicated Melee character.
3 – The Shield Eternal — Not much needs to be said about this one, as anyone who has played even a little 40K is likely familiar with it. For the price of 10 MBs you get a 3++ save, Eternal Warrior, and Adamantium Will (which affects the entire unit the character is in). Despite being expensive, this is still an outstanding Relic, especially for a Chapter Master geared toward close combat or a Librarian with Terminator Armor and maxed out Biomancy rolls (imagine a Librarian with a 2+ save from TDA, a 3++ save and EW from the Shield Eternal, T7 from Iron Arm, and S9 AP2 striking at I4 from his Force Maul and Iron Arm). The classic build for this relic is an Iron Hands Chapter Master on a Bike with Artificier Armor, a TH, and the Shield Eternal; attach him to a Biker Command Squad with an Apothecary and you have a 2+/3++ save, 4W, T5, Eternal Warrior, FNP(4+), IWND bruiser with 5 x S8 AP2 Concussive attacks on the charge!
4 – The Burning Blade — The other iconic Relic, this melee weapon costs 11 MBs and gives its bearer the ability to strike at S7 AP2 while swinging at full Initiative (so I5 for Captains and Chapter Masters). The Burning Blade also has the Blind USR (great when attacking a horde of Orks or Necrons) and a small down-side in the form of the Incandescent rule, which means on a roll of 1 at end of any assault phase in which the character attacked, he takes a S4 AP2 hit. Given that most ICs bearing the Burning Blade are at least T4 and have a 4++ save from their Iron Halo, this means that the blade will only wound its bearer about 5% of the time (even less if the character has T5 and/or a 3++ save). Altogether, this Relic is best used, I think, on a model who is leading a squad with a lot of AP4 or worse attacks (say an Assault Marine squad or a Crusader squad with BP/CCWs), since it balances the “torrent” of attacks with some high Strength, low AP attacks that can deal with tough enemy units or help its bearer win in a challenge. Don’t forget that the Burning Blade is not a Specialist Weapon or Two-Handed, so its bearer gains an extra attack when it is paired with a BP, Plasma Pistol, etc.
5 – The Armour Indomitus — A suit of Aritificer Armor that confers a 2+ save (with none of the benefits or drawbacks of TDA) and a 6++ save and which costs a whopping 12 MBs. Once a game, for one phase only, it can activate a 2++ save for the bearer until the end of that phase. Overall, I think this Relic might be a little too pricey for what it brings to the fight, especially since normal Artificier Armor is only 4 MBs (you are paying 8 MBs for a 6++ save that, once a game can become a 2++ save), but if used correctly that 2++ can be a game winner (i.e. imagine your Chapter Master storming into you opponent’s Hive Tyrant Warlord, activating the 2++ save, brushing off all the Hive Tyrant’s S6 AP2 attacks, then beating him to a pulp with his Thunder Hammer). Overall, probably the worst Relic option, but still useable in the right circumstances. Note that, while you can only take one Relic Weapon per character, an IC can take the Armour Indomitus and still take another Relic (unlike all the other ones).
6 – Standard of the Emperor Ascendant — For 12 MBs, one Command Squad or Honor Guard squad in your army can take this Relic, granting the bearer the Fear USR and providing a very potent force-multiplier “aura” to all friendly models from the same Chapter within 12″. Specifically, it grants all friendly models within 12″ Fearless and +1A (note, this is MODELs, not UNITs, so you can’t just have a single model from a unit within 12″ and give the +1A to everyone in his squad; Fearless, does however “transfer” to the entire squad even if only one model in the squad in within range of the Banner carrier). While not cheap by any means, this can turn mediocre combat units into serious combatants and take dedicated Assault units and make them absolutely devastating. This Relic combines especially well with a Reclusiam Command Squad (the Chaplian gives out Hatred to units within 6″ and the Banner gives out +1A to models within 12″), with Pedro Kantor and an Honor Guard escort (between Kantor and the Banner, you are providing +2A attacks to all friendly Crimson Fist models within 12″), or with Chaplain Grimaldus, his Servitors, and a Command Squad (Grimaldus and Servitors provide Zealot and FNP auras and the Banner provides a +1A aura; taken all together and you can make nearby Crusader Squads hit like a ton of bricks).
Overall, I would assess the Space Marine Relics as generally quite useful and competitive, with each one being useable in its own right, though the Armour Indomitus really is a bit expensive for what its does. Compared with the Relic options in other armies, the Adeptus Astartes have probably one of the better selections on the game.