Been playing the beta for a few hours now and it looks really awesome. Graphics are slick, gameplay is smoothe, the game looks polished overall and behaves like you would expect. UI is customizable as well.
What I really like is that you can really customize the type of build your character has. In wow you have 3 trees per char, and they are set per class.
In Rift you can choose which three trees (called souls) you get, based off your your primary class (warrior, rogue, mage, cleric).
Want a warrior with a pet and healing abilities? That's fine! A priest (cleric) who can tank? Sure! Couple of limitations apply to make sure you can't be OP though
Some souls are limited to certain primary classes (only warriors can be paladins f.e.)
The Rift invasions are pretty cool too. If they are left unchecked, they grow in power and start to take over towns etc
You get rewards based on your contribution (dmg/healing done), so you don't have to make a raid or be annoyed that someone else is tagging mobs.