Strong story, role playing, tactical combat - the spiritual successor of the baldurs gate, icewind dale etc games.
So, you have to learn a new combat, class system. It takes a while. You also have to learn how to create tactics for your party members. Its a long learning curve, but ultimately worth it if you're in the right state of mind. This is really a game for people who can marinate for hours in the tolkien/dnd fantasy world thinking.
Immersion is greatly increased by the very strong backstory and role playing elements. Great care has also gone into personalizing each character. Huge and very impactful spell effects are a great draw for this game after the lackluster ones of so many other games. The graphics and character rending is absolutely top notch. Monsters look really cool and deserving of some serious punishment. Your own character and companions look wonderfuly lifelike and can be extremely customized. Sounds and voice acting are likewise excellent. There are also some solid and gratifying death animations.
Immersion can suddenly die however when you realize you have missed some really key learning of the system, have to pause suddenly in the middle of battle, or restart from your old save game for the fourth plus time. The maps are also kinda small, albeit packed with stuff.
There is an extensive crafting system if you like that sorta thing. Its ok i guess. The additional content is quite good and there is a fair amount of it.
good job ea and bioware. two of my favorite companies.