Played this yesterday, some thoughts:
-Game looks great, no complaints here.
-Haven't encountered any bugs so far aside from a missing reference in the combat log. And the game plays great even on my crappy laptop. Short load times, not a memory hog, can alt-tab in and out instantaneously, no frame rate drops, etc.
-Definitely plays like an IE game in terms of moment-to-moment gameplay outside of combat (exploration, dialogues, looting, etc.).
-I like that it appears to have taken the BG1 approach towards the world map. Even if BG2 was a tighter experience overall, I always missed that element going out and finding areas on your own.
-Game takes a leaf from KotC et al's book and gives you links/tooltips to find out more specific information about what abilities do and such, which is good. However, it's a bit inconsistent about it. There have been at least a couple of times where I've moused over some opaquely-named ability to find out what it does, but the game doesn't give me any more information. Also, the journal seems to be missing some obvious entries under the combat section, such as "sneak attacks". Might have just missed it though.
-Started a game in expert mode, but I think I'm going to disable it that means I'll be able to see an indicator for the AoE of my spells and combat abilities. Giving you that information was one of the very few improvements the NWNs made over the IE games, and it's doubly necessary here since AoEs can vary in size based on character stats.
-Obsidian included a lot of options to let the player configure how the game plays (e.g., toggles for whether you're given information about the requirements and effects of dialogue options), which is a good thing that goes overlooked by a surprisingly large number of developers.
-Combat felt rather clusterfucky at first, but it was a bit better by the time I got used to it and gained a few characters. I'll withhold judgment for now, especially since low-level combat often doesn't reflect the quality of higher-level combat in this sort of game.
-The combat log seems to be missing a lot of information that ought to be there. For example, sometimes I'll use a spell, and it'll say that I hit 3 enemies with it, but there won't be any indication of which ones or how much damage it did. Also, it's a minor annoyance, but it would be nice to be able to select a character through the combat log, especially since you have to expand it to 3+ times the default size to get much use out of it.
Only had a short while to play (got to Gilded Vale, picked up a few characters, and did the quest for Calisca's sister), so these are just my first impressions.