Albeit EE doesn't differ from the original much, it does in some significant ways. First of all, it allows running the game in high resolution. You can do it with the old BG too, but that requires a mod, and it's a nice thing to have it without doing anything. EE adds some magical weapons and other items to the game too. Not too many, which is very good, and they are balanced and fit in the game. Moreover, unlike vanilla BG, EE is not limited to Windows only, and can be run on other operating systems. A great thing is also the fact that BG EE has many languages to choose from (albeit no dubbings) so it might be a good way to practice one's language skills. Unfortunately these are the only positive things I can say about EE.
When EE was released it was full of bugs, even gamebreaking ones, but they were fixed by now. Most of them at least, because some things remain broken. For example I couldn't join Alora to my team, because her encounter was broken. Moreover, the quality of the writing when it comes to the new dialogues (and NPCs) is low, and it stands out from the rest of the game, definitely not in a positive way. Hence, it's better to play vanilla game without it. Moreover, for replayability there are many interesting modifications for Baldur's Gate, but they do not work with EE.
Play Baldur's Gate if you haven't already. To decide whether to choose BG:EE or BG you should consider quite a few things.
Why choose BG over BG:EE?
- no bugs
- quality of the game is the same all-through
- modifications
Why choose BG:EE over BG?
- multiple language versions (but no dubbings)
- multiple operating systems supported (albeit Wine runs BG just fine)