Reasons to not play BG1:EE - it was a bad EE overall, new UI is bad, it converts the game to the BG2 engine. BG1 had better avatars, and the game was balanced around the stock classes, weapon proficiencies and spells. Screws up the spawning system. Bunch of other minor reasons, but those are the main ones. Oh, new characters and mod are pointless/terrible.
Reasons to not play BG2:EE - I already have a perfectly good modded BG2. Do not want to spend $20 on something that I already have.
Reasons not to play IWD:EE - converts the game to BG2 engine, once again messes with balance/systems. Uses BG2 avatars, when 1PP mod for IWD1 ports back in the much better BG1/IWD1 avatars. UI is see through and not full screen.
Oh yeah, zooming in below source resolution on 2D art is retarded.
Uh no, it uses the IWD1 avatars actually.... I agree the zooming in super close is dumb, but the zooming super far out is nice. The UI not being full screen is hardly a bad thing, not that there is a ton of dead space, just two tiny bits at the bottom. The BG2 engine is also better than the IWD1 engine and some of the options (like rogue sneak attacks) you don't like from BG2 can actually be disabled.