I found the RAW vampire to be perfectly functional. Mind you, I only got it to 14th level. But in a stealth party, the variety of skills was wonderful. Especially once he had bat-form and could scout the area, report on the next encounter, fly back, and then fly in and start from whatever spot he wanted. Sure, it took a couple of short rests, and if there was anything with true sight or that would actually be interested in eating bat, not so hot, but for the vast majority... Also being able to push and pull at-will...
No, the only thing really missing from the RAW vampire class was magic item support, because WotC had already decided to end the edition and market to 5th ed.
It is functional for sure, I think it got too much negativity in the beginning and people were underestimating how good it is to be able to not need healing surges yourself.
It just has some things which feel a bit clunky or which make you feel squishy like:
- You have no use for constitution, which makes your HP in low levels quite a bit weak. You can choose one of the backgrounds to fix it, but it should not depend on a specific background.
- Level 3 to level 7 you have 1 way to spend a healing surge but only 1 way to get an additional one, making that option more of a trap. (Which makes a lot of people multiclass and trade the level 3 with another classes power)
- The level 5 ultimate which is risky, but really interesting, never improves which is a bit of a shame
- The level 9 ultimate which is cool feels feels always a bit bad in the sense that you need to
- the level 13 gives an additional healing surge, but because of your level 1 passive you never want to use your own healing surges anyway.
- The really cool level 16 utility power needs a standard action (instead of a minor similar things normally use), which again as a striker you dont really want to use.
- There is no real damage increase from level 12 until level 17, but than at level 17 there is a huge powerspike.
- One of the 2 paragon paths has a really really bad ultimate ability (at level 20) not fitting a striker at all.
I really think the vampire is a cool class, and agree that it is functional (no idea why so many people thought it was not), there are just some small tweaks which make it from a cool "functional" class into a cool great class.