Least your entire class wasn't nerfed to the ground because of PvP.

None of the 51 point talents are really all that amazingly awesomely epic. In general, they are situational.

I've found Dispersion to be quite useful in BT and MH. I've also used to solo/duo a number of bosses and/or elite mobs ( e.g. that one you have to kill for Dirge's Kickin' Chops ).

Not as good or critical as, say, Shadowform but I think it serves a purpose at least.

I dont see how the new mana regen can be "awful" by any stretch of the word.. you get the same amount of mana back in the same amount of time, except you ALSO get some of it *earlier*. It's a complete buff to mana regen across the board

Let's say I dislike the fact you're now obliged to use Mind Blast and reduce its cooldown, I prefered the old version with dot ticking mana regen.
And I also dislike the fact that a lot of 51pointers are more situationnal. The majority of x1 talents almost used to be "no brainer".
This could lead to more types of templates, more "hybrids", but generally the last tiers of talents are pretty good, meaning you end up with 50+points in a tree which leads to a "hmm ok, I'll take the 51st".
So far and correct me if I'm wrong, the only class who seems to benefit the more from hybrid build is the DK.

Actually, it doesn't return the same amount of mana. If you were clever about how you applied VT and used downranked DoTs and flay, you could chain up mana-positive rotations on mobs. Pre-3.0.2 I'd take 3 of the Wretched Fiend/Devouers in Q'D Isle on at once and be close to 100% mana once I was done.

The thing is, before downranking was removed you could do a lot with VT, now you can't. In fact casting VT+MB now will always cost more mana than you get back from Replenishment, even if you are a level 80 Spriest in 25-man epics. It is a group utility spell, it isn't there to replenish your own mana. If you want to replenish your own mana while casting, unfortunately your two choices are:
1. buy up Imp Spirit Tap and crit a lot (RNG dependant)
2. buy up Meditation in Discipline (lose Shadow points)
3. stop casting and wand (cruddy DPS for a DPS-only spec)
4. pop Dispersion (stop DPS for a DPS-only spec)

or.. secret option #5, reroll a ret pally since even with the 'nerfs' they can, with mixed epics, blues & greens, put out more damage than an epicced-out Spriest in 3.0.2 while dropping their mana bar no lower than 85%.

51 point talents aren't "press [key] to win" talents on any class, on any spec.

Take Hunger for Blood - 9% flat damage buff is nice, sure, but it's a PITA to keep running and it's certainly not a game changer.

Suck it up! You really do have to learn to use the whole class, not just a win button.