The sheer production value, especially for an crpg like fully voiced characters, mocap, tons of great cutscenes, the epic, cinematic feel of the game...
The amount of freedom you have in exploration and combat, feels like a big sandbox to toy around
The combat, while I find it to easy and not every encounter is well made, I really enjoy it. Part of it is due to visual and over the top sound effects
A lot of the environment design, especially in act 2, along with the monsters / enemies
Lots of memorable characters with amazing voice actors. Shadowheart is amazing, Raphael, Lae'zel... the characters are written in a way that I emotionally react to them e.g. I hate that vampire dude with a passion, if he wouldn't be useful from time to time I'd stake him 10 times over
The overall complexity of the game, I don't like streamlined games, I like something to sink my teeth in, especially into build making
