We can't convert these spells:
Wall of Moonlight
Mordenkainen's Force Missiles
or the scattering of items that rely on them. We use the BG2 versions of Chain Lightning, Incendiary Cloud, and Power Word: Kill. The conversions of Static Charge and Cat's Grace aren't perfect, nor are the conversions of Edion's Ring, Kossuth's Ring, and Kontik's Ring. All other spells and items are converted (let's not talk about bugs...)
We can't convert the White Dragon animation, so we use the BG2 Silver Dragon
3) Death of Player 1
If Player 1 dies, the game ends (and the Bhaalspawn death movie plays). We don't know a way around this (it's unclear if it's even a good idea).
4) Transition between IWD and HOW
We can't change the world map mid-game (not reversibly, anyway), so we have one world map for both (we've glued the two maps together and added a border). You can still start a HOW-only game, though (in which case you get the standard world map).
We can't currently reproduce the pretty IWD area-specific loadscreens.
6) Character progression
We can't reproduce the druid's Timeless Body power, or the thief's Evasion, Crippling Strike or Sneak Attack powers. (On the other hand, thieves still get their BG2 powers, i.e. trapsetting and detect illusion). We do reproduce the ranger's Tracking ability, but not perfectly (it includes the BG2 ability to detect where enemies are, so it's a bit more powerful than in IWD.)
I *think* that's it, though I'll post if I remember anything else. (And of course this doesn't cover bugs; that's a whole other story...)
[Edit 3/10/2010: this is a bit out of date; I'll unpin it and do a new one in due course]
Edited by DavidW, 03 October 2010 - 09:07 AM.