DubConqueror: In discussions you'll see often mentioned that all the Enhanced Editions of the Infinity Engine games (BG, BG2, IWD, PST) have to offer is widescreen support, that can also be done by mods, but this is false information.
One of the most useful improvements over the original games is the portrait icons showing what the next action is a character will be performing. When you order an action to a character, such as casting a certain spell, the character will not perform that action instantly as the time in combat is divided into rounds and that rounds into segments (indicated by the speed factor) and wether a new round for that character has already started and the speed factor of a weapon or casting time of a spell (0=instantly at the start of the round, 10=a full round) determines when the action will be taken.
So time will be spent waiting for the character to cast a spell. When an action is taken, it's shown in the combat log, but this can scroll by quit quickly in a big fight. With the old game, I found myself repeatedly giving orders if I didn't know if I had already given the order or if it was already done, but with the Enhanced Edition, you can see at a glance what the next action is that will be taken by the character in question.
Another useful thing especially if you're new to the game, is then new character screen that breaks down the stats for to hit chance and armour (now as Thac0 - to hit armour class zero - and AC - armour class) respectively. The weapon itself, bonuses, a character's STRegth and DEXterity all influence this. In the character screen of the Enhanced Edition, you can see how all these factors for the equipped weapons and armour influence the stats.
Non of these can be found modded into the classic versions. The Enhanced Edition made it far easier to mod the originals as well, giving modders far more freedom to things that formerly where 'hard-coded' and couldn't be changed.
*edit: a third very useful feature is with the Enhanced Edition you can switch between wielding a weapon used with two hands (a two-handed melee weapon or a bow) and wielding a shield + one-handed weapon without the need to go into the inventory and de-equip all two-handed weapons in your quickslots before equiping a shield and vice versa. In classes Baldur's Gate 1 this last feature was especially annoying as the game un-paused when going to the inventory, but even with classic Baldur's Gate 2 this was a nuisance.
From what I here, there is one possible (and easy) improvement that should have been in the EEs, but wasn't; in the games, when you die, you can't look through the combat log to see what kills you. This is incredibly frustrating, and means that you can't easily learn from your mistakes.
(This isn't usually a problem in turn based games because you usually see actions one at a time while waiting, so you are unlikely to miss the attack that killed you (and some roguelikes let you view the combat log after death), and it isn't as big a deal in the Icewind Dale games, as the game doesn't end until your *entire* party gets wiped out; it is, however a big issue in Baldur's Gate 1 and 2, and one of the many regressions compared to classic RPGs.)