I've played quite a bit of it, people compare it to D2, but I feel it's more akin to D1. The mechanics and animations are a bit clunky, but it's a lot of fun once you get used to it. There is quite a lot of diversity at the low levels (the ability grid is huuuuge and quite daunting the first time you see it), which is awesome, but once you get 70+ and start doing maps, the choice of possible specs narrows down quite a bit in order to be viable.
The real selling point to me, is the "races"/challenges aspect.
It's basically a fixed timeframe (1 hour, 3 hours, 6 hours etc.) race with specific modifications to make it different than the main game with leaderboards.
For instance you could have a "Bloodmagic turbo 3 hour race" which means that you don't have mana, but all skills take some of your life instead, and the monsters are 25% faster and the ranged mobs shoot 3x the normal amount of projectiles.
Some of them are too much of a time commitment for me (24 hour, 1 week etc.) but it can really be a lot of fun.