Your basic perk. If you use two-handed weapons with any regularity, take this and get all of it. Story over, move on.
If you’re lucky, you don’t use power attacks a lot. That doesn’t matter much, though, because the really nice perks for two-handed weapons here require this perk anyway. And, with no off-hand, you have no option for dealing with a blocker other than power attacking to break the block, so go ahead and grab this. It’ll save you a lot of time spent hammering away for no effect, and a lot more time waiting for your stamina to return so you can cut another big chunk out of your target.
This is not as good as another rank of Barbarian. I will repeat that- this is not as good as another rank of Barbarian. On average, taking all three ranks of Deep Wounds will still help less than a single rank of Barbarian. Not that it’s bad, it just isn’t as good as it could be- even not taking into account that it’s a greatsword-only perk. Found a better axe than your sword? Too bad.
Also not as good as another rank of Barbarian. More interesting, though, in that it basically makes all your two-handed axes mildly poisonous, causing bleed damage for a short time after each hit. Not terrible, but not great.
This does nothing if your opponent is not actually wearing armor. Trolls don’t care about this, giant spiders don’t care about this, giants don’t care about this- the list of things that don’t care is distressingly large. Fortunately, the enemies that do care about this tend to care a lot about it. Might be worth taking and having a warhammer on hand at all times.