Blood has fast become the "imba" tree of repute, but what's probably better to say about is that it is an "easy" tree, in that it combines high survivability with a respectable amount of DPS. The massive amount of healing power is what provides the survivability, while talents like Might of Morgraine and Dancing Rune Weapon provide the massive amounts of burst damage.
Before the latest nerf, it was phenomenal. You could use it solo even major elite quest mobs such as Tusker. Simply apply Mark of Blood, keep Rune Tap ready to use for emergencies, wait for Bloodworms to come up, and apply Vampiric Blood for the maximum health gain. As soon as you had 100 runic power and a couple diseases up and a few blood runes free, you could summon a Dancing Rune Weapon and put out a stream of Heart Strikes for massive damage, then Obliterate for even more damage, especially with a Might of Mograine enabled critical strike.
Now, to be honest, this is still a very viable damage setup, there's just been a good set of nerfs, with some cooldowns tweaked and some abilities revamped. Some of the biggest changes:
Might of Mograine: Obliterate was removed from this skill. Now, the massive obliterate critical strikes -- some were reporting crits as high as 8k damage -- are gone. I'm honestly OK with this, as I think it brings Blood specced Obliterates down to in-line with the Obliterate potential of other specs.
Bloodworms: These were nerfed to 9% chance to proc (from 12%), and do much less healing. Also, the talent gives you this annoying permanent poison cloud aura.
Dancing Rune Weapon's cooldown was nerfed to 2 minutes from 1 minute. On individual elite battles, this probably still doesn't matter as much, but it definitely leads to an overall DPS decrease.
has been nerfed to give 2% of damage back as health instead of 4%. Neither number is much, technically, but we're talking the healing cut in half. It's actually more noticeable than I first thought.
has been changed to give all party members 2% of their damage back as health -- meaning a Death Knight taking this can get their old Blood Presence back, but no longer gets any extra healing from Blood Aura. It also means that healers will no longer really see any benefit from Blood Aura unless Wrath
healing is so easy that they find themselves nuking in between heals with their new unified spellpower.
Heart Strike has been bugged so that it no longer gets a benefit from Sigil of the Dark Rider
(or vice-versa). This means that Blood Strike
is now better for PvE, but still doesn't have the bonus damage of the old Heart Strike.
All of this combined together has put a crimp on Blood soloing to some level. I find myself using Rune Tap and Death Strike a lot more often to push myself back up into Blood Gorged territory, and on battles where I'm unlucky enough to have no Bloodworms proc, it's sometimes a little hairy, especially when I have multiple mobs, although Pestilence and Death and Decay do help there somewhat, especially with a few points in the Unholy tree.
Still, I find Blood to be a viable tree still, and incredibly good for soloing with low downtime and some very handy emergency buttons. I do appreciate that it's less of a clear choice over Unholy now, especially since Unholy is my favorite tree and the one I currently plan to spec at 80. Now it feels less like Blood is the overwhelming choice for easy leveling and more that both trees have their advantages.
Blood In the Future
Still, I'm not saying that Blood is perfect either, and there's a few areas where I think they may not quite have the right balance for certain talents.
Mark of Blood, for example, really doesn't feel like it's quite where it needs to be. 2% per a hit sounds nice, and it is when you're dealing with a fast attacker. With a slow attacker, that 2% doesn't do much at all. Really, though, if the 2% stays, it's probably fine, but bumping the cooldown down to 1 minute would at least allow it to be more usable for tanking rotations and upgrade it to valid small utility from a gimmick used to take down quest elites in solo play.
Improved Rune Tap is already sort of nice, seeing as it essentially gives you a 30 second scaling personal healthstone, but I'd honestly like to see the extra health bumped up a bit. Allowing a full Improved Rune Tap to heal you for 25% of your maximum health would keep it competitive as mobs get more elite and hits get more punishing as we level.
Bloodworms still feel like they need to find their post. Currently, I think nerfing both their damage and their chance to proc has underpowered them, and that it'd be nice to see them back to 12% chance to appear. The other possibility is to scrap the idea of Bloodworms altogether and simply turn the talent into a weapon proc that steals a certain percent of weapon damage as health -- That is, it does a percentage of extra damage and heals the Death Knight for that damage.
Of course, the above weapon proc could also simply be made one of the new Runeforging enchants, which I actually like the most, since it gives the other 2 talent trees the chance to get some of Blood's incredible survivability and allow them a way to be a little less dependent on Death Strike.
I'd also rather like to see them unnerf Blood Presence, if only because the nerf was a little unfair to Frost and Unholy Death Knights who otherwise rely primarily on Death Strike for their healing. Similarly, Blood Aura could use some adjustment to be fair to healers without overpowering the Blood Knight. It might be as simple as something like "the healing done by Blood Presence is also healed to the Death Knight's group members." Thus, the Blood Death Knight is not given any benefit that might make it overpowered, but the talent is still probably worth picking up for grouping Death Knights.
Really, once Blood gets a few more tweaks, I think it will go back to feeling like the most complete and sane of the three currently in Beta. Even with the nerfs, it still has a lot to offer. Of course, things are likely to change even more in Beta, and hopefully we can make some sense of it for you once the dust falls out. For now, I'd say leveling as Blood is still a pretty safe bet for any Death Knight, even if you may have to call in some help for Tusker after all.