What is good in BG1 that is bad in BG2?
Welcome back, Excidium! On topic, a few things:
1) Better over-arching world structure. While both games aim to portray a region of the Forgotten Realms (Sword Coast, Amn respectively), because of its freedom, BG1 actually feels like a region, a continuous slice of the world. You can go from any map to any adjacent map, barring plot restrictions. In BG2, you cannot do this, as most maps require some particular quest or plot-point to activate. So BG2 has a hub structure, where you go to the quest-hub, pick up the quests, go somewhere else, come back to the hub, etc. This really makes it feel much more linear and less of a representation of an actual region.
2) All the advantages of revolving around a low-level party. Better loot itemization, as finding a magic item actually feels special, as opposed to BG2 where you are swimming in magical things from the opening dungeon. More balanced spells, stats, abilities, etc. A world that actually feels more real, because you have peasants and bandits, as opposed to BG2 with its running into a dragon or a demi-lich or a downed spaceship every two steps.
3) This is a bit more subjective, but in my opinion, a better story. The whole mystery of being pursued by assassins while investigating the iron shortage that eventually turns into Iron Throne's political intrigue and finally Sarevok's plot and your true heritage is way more interesting than following some crazed elf around as he is dealing with his revenge issues.
