I made it into the beta weekend a while ago. They actually stretched it all the way to the thursday after, so I had a lot of time to play.

The outdoor areas are pretty big, it's nice to explore them. They have some randomly generated stuff on there as well. I also noticed a very large variety in monsters in the 4-5 hours that each playthrough of the beta lasted approximately. I hope they can keep up that variation during the entire game.
Combat feels great. Especially the Ember Mage, the magic is awesome. Even the basic spell you start out with is nice. The Berserker is also pretty crazy after you get a few skill points in the right place, you just smash things to pieces while dual wielding weapons. The nice thing about melee weapons is that they all hit in an arc, even the basic attack. So if you're carrying a big weapon and swing it, it can hit multiple enemies at once instead of just one at a time like in TL1.
Remember how you could send your pet to town to sell all the loot? They now also have a shopping list, so you can buy some basic items (health/mana potions, portal/identify scrolls) without leaving the dungeon you're in.
There are some nice small improvements over the original game: The UI can be scaled and some elements can be hidden. Also In Torchlight 1 every hit you do would show you how much damage it did, so if you did a big AOE attack the screen was covered in numbers. In Torchlight 2 there's an option to change the frequency at which these damage numbers appear. Also items can be identified by right clicking on them directly, which will consume an identify scroll.
Also: Customization of your character's looks and more pets.

I can't wait for the release.
