Simple question, with probably a complex answer, just downloaded Icewind dale complete which I own, and immedately remembered why I regretted buying the game so does anyone have a detailed list about the enhancements, particularly related to classes?

(I still can't believe a a fighter/Mage/theif can't use theiving skills in studded leather, or not use magic, in Armor, I mean what's the point then?)

The Enhanced Edition is based off the engine used in Baldur's Gate 2. This means that you get many of the features of BG2, including additional classes, kits, and spells. (For spells that exist in both BG2 and IWD, IWD:EE uses the IWD version, so Mordenkainen's Sword isn't a summon, and Horrid Wilting will hurt allies, for example.) It also means that you get true dual wielding, but that means that Rangers lose their extra attack they get in the classic edition when not using a shield.

Whether or not this is balanced is an interesting question; my understanding is that the AI, for the most part, doesn't account for the new spells. I believe some players might see these changes as making the game too easy.

Also, a F/M/T might not be able to use thieving skills use magic while wearing armor, but she can do so while under the effect of a spell like Armor or Shield; hence that triple-class can still be useful. Also, if you get lucky, it's possible to get elven chain mail, which allows spellcasting (I'm not sure about thief skills) despite being armor. Unfortunately, it's random whether it appears, and there are only a limited number of opportunities to get some, so there's a good chance that you won't be able to get it. (I really dislike non-respawning treasure in games like this.)