I could go on forever, why I prefer the first game and why the sequel is one of the biggest disappointments, but since that is quite an old thread I would like to just add one bit:

BG2 has move advanced graphics, apart from horrendous and mirrored character animations + those ugly paperdolls and item icons. One of the worst cases is that swing with two handed sword, where if you look closely the character's knees are touching the ground. They really move like they are made out of jelly to me.

This is a good thread (even if it is old). Anyway, here are some of my thoughts:

I actually wasn't able to really get into either game. Part of the problem was the real time with pause combat, which really doesn't work for me (I would rather have turn-based combat for this sort of game), but there were other issues.

BG1: The biggest issue is that, at level 1 (which you are stuck at for far too long), combat is just not fun. It feels like every single attack (whether by a party member or by an enemy) is a low accuracy instant death attack, which makes things rather frustrating, as your attacks keep missing, and then an enemy kills you with one hit. The final straw, when I tried playing this game, is when I (at level 1 IIRC) encountered an enemy that used Improved Invisibility; how am I expected to counter that? (I personally think that spell (and similar spells) shouldn't have been in either game, even if it's easier to counter in BG2.)

BG2: Bimlanders's comment about BG2 quests is probably my biggest issue with the game; I would rather seek out quests, rather than have the quests seek out me, especially given how unmanageable it gets. (The only other time I've seen this sort of thing was in Asellus's quest in SaGa Frontier, and even that wasn't nearly as complex, as it basically amounted to sudden boss fights while exploring rather than having to keep track of entire quests.) I enjoyed having high level magic, though I think the game could have been better without as many immunities and specific counterspells (get rid of both Invisibility and True Seeing, for example), and without the spell disruption mechanic.

Also, pathfinding problems have been mentioned. I think the problem isn't so much the bad pathfinding, but more the fact that the player is forced to rely on it; you can't just move your party directly with the arrow keys (which instead just move the camera). If it were possible to control the characters directly (rather than just clicking somewhere and having to rely on the pathfinding), there would be far fewer complaints about it.

This is more or less my biggest complaint that applies specifically to BG2 (as opposed to the general issues I have with both games, like the combat).
I think the problem isn't so much the power, but more the fact that the game mechanics don't make it easy to manage such levels of power. For example, I think the magic system would be better, particularly at high levels, if your magical resources weren't segregated by level. As it is, you have to worry about low level spells; if the game used a spell point system, you could just ignore the low level spells (except those that are particularly useful, or if you want to conserve SP), and just focus on the spells that are actually useful. No need to worry about spells like Cure Light Wounds and Reflected Image at high levels.

There's also some scaling issues; the fact that both fighting skill and defense are reflected in chance to hit also causes issues. At low levels, attacks miss too often, and at high levels, AC (and therefore most armor) becomes useless. IMO, it would be better if attacks hit nearly all the time, and if skill and defense would be reflected in damage rather than accuracy. I can actually think of a few games that actually take you to different planes.

One example is Bard's Tale 3. Once you get past the pair of starter dungeons, you will need to change one of your casters into a Chronomancer, who can then use spells to travel to different planes (albeit only one at first). (Note: Stay away from the DOS and Amiga versions, as those versions are rather buggy in a way that makes the game less fun. Stick with the 8-bit versions.)

From what I hear, Pools of Darkness also takes you to different planes.

(Note that both these games are high level adventures; Bard's Tale 3 isn't AD&D based, so it has very different balance properties, for example.)

It doesn't have to be that way. SaGa Frontier, for example, features overpowered items and skills (there are a few spells, like Overdrive, that would be considered to be around 9th level in AD&D terms), yet the setting still feels like a prominent feature of the game. Perhaps it's the fact that each region is very different, with areas ranging from high technology to farmland to medieval Japan (in ruins) to a forest town with a European-style castle (with a bit of a vampire story feel). There's even both surreal magical areas and virtual reality. As you can see, this is a much more varied setting than the Baldur's Gate series (which never gets into modern or future levels of technology), and it feels rather central to the game, even with all the overpowered stuff in there. (Also, the fact that your resources are segregated by type rather than level means that you don't need to worry about weak abilities later in the game.)

(SaGa Frontier is one of my favorite games to use as a point of comparison to the BG series; the release dates aren't *that* far apart, both games are RPGs, and yet the games are *so* different.)

Actually, that's one of the issues with the high level game: you end up using the same handful of spells over and over. The vast majority of your low level spells are ignored completely, so those spell slots are just filled up with spells that re never used (or you can just not even bother filling them at all). I guess a spell point system may work better in that regard, as you could just use the points for higher levels spells only and get a few more castings.

Regardless though, for various other reasons the higher levels don't really appeal to me at all. It's not nearly as fun for me to play a character that's practically god-like than it is to play one that has only moderate powers.