For me, Diablo III blows this away from a gameplay perspective. Maybe I just picked a boring/bad class that needs some patching. Whatever the name of the Spellcasting Mage class is in this game.
The spells seems super underpowered, I've been leveling up almost nothing but Force and I just run out of MP super-super quick without seeming to do any decent amount of damage. I end up doing way more damage without worrying an expendable resource by melee'ing and I'm not even putting any points into Strength. Just seems imbalanced. Also the spell trees are boring, no spells seem very interesting or powerful. Every time I level up it's just like "meh", where as in Diablo III (or any Diablo, really) I was excited to level up and see what new spells I could learn or enhance. They all seemed unique and useful in different circumstances and were fun to combine, seemed to require a bit more skill, even as low as Level 21 where I'm at in TL2 right now. Again, just first impressions, maybe the class will get cooler as it goes on.
As I've said before, great game, especially for $20. But I think it's kind of an unfair comparison to Diablo III, a $60 game. Diablo III just blows it away in terms of polish, graphics, and playability. But hey, it's $20, and it's probably the best budget game I've ever played.