I would like to see:
3rd Edition D&D rules (I'm not familiar with 3.5, so I can't speak for it)
A few kits for each of the classes, and especially the choice to be a Wild Mage.
NPCs that have personalities, dialogues, opinions, form relationships and friendships with each other and not just the PC. I'd also like so enough so that all the basics are covered (I sorely missed an evil thief, or a pure thief that you could keep for that matter, in BG2). As its been said, it must be alive.
Game length, somewhere in between PS:T and BG2.
Start at level one, and the level cap at around level 20 or so. And do it Throne of Bhaal style, meaning its actually very, very hard to hit the cap. Preferably, most parties would finish the game around level 15 or so. This means lots of low leveling (which can be quite fun, since you'll battle normal enemies that everyone else does, like Orcs and such). A good example of a low level game would be Icewind Dale, which did that perfectly, IMO.
I don't care excessively about good graphics. Icewind Dale was much more beautiful than many 3D games I've seen, and BG2 had a very nice feel to it that other games didn't have. Spell animations would rock, though. Those in BG2 were rather boring, compared to a game like Icewind Dale (or the cutscene spells from PS:T). Liked how in Icewind Dale a fireball didn't do instant damage to everyone...a character with the Boots of Speed could potentially outrun the expanding fireball. Not to mention that the fireballs in IWD look awesome.
The ability to have a party of 6 that you can control. This was the main drawback from Neverwinter Nights in my opinion.
Few uber-items. For me, BG2:SoA did this almost perfectly. There were only a few +4 or +5 weapons in the game, and most (Carsomyr or Crom Faeyr) were hard to get. It should stay like that. If there is an expansion coming out, then either only add one or two extra items or don't add them at all. My largest gripe about ToB is the abundance of uber-items.
Good portraits. I largely disliked many of them from NWN, liked most from BG/BG2, and I loved the style of the IWD ones.
A storyline that is related to the Bhaalspawn saga (so it won't be some cheap corporate trick), but that obviously doesn't continue it.
I don't really feel a need for more races...
Just my 2 gp.