Some time back on the gibberlings3 forums someone uploaded all of the outdoor maps of BG1 next to one another, and I was surprised when I realized that, they made up an almost complete, huge map.
Yes. That's not particularly impressive IMO, but it is impressive how well Bioware guides players - sure you can go any direction, but players are skilfully guided in the right direction.
There are also attempt at Ultima-like simulation - with guards being called when you are stealing, or bigger differences between nights&day.
I also agree that biggest flaw of BG2 is a sheer amount of optional side activities players can get lost in and forget about main motivation of our character.
There is however plot and there is character and world building - and the sidequest fulfill those well. Not to mention that it is in BG2 where companions, became companions. That's something that made RPGs like that come to live.
It is overall a more sophisticated, and polished experience, which focuses on things BG1 was capable of doing well (unique handcrafted locations and story) and ditching things that it didn't ("world simulation"). I like to think of those as low and high level adventure. With BG1 focusing on us dealing with mundane problems and fighting off wolf's, while as higher level party you get to do cool stuff and traveling is reduced to the interesting snippets through random encounters.
