I chose to play the Assassin as I held a controller in my hand, but for the PC version of the game and had a Gearbox Dev as my co-op partner. The Assassin, Zero is the equivalent to the Hunter of the first game. It very much is "more Borderlands" but feels tighter and they expanded the trees to have branches that can diversify the characters and make them just as random as the weapons that drop. The skills you select can compliment each other between branches.
The quest I played involved escorting a large robot to come destroy some propaganda statues. While you might be groaning at this, it was the most enjoyable escort mission I've played. I don't know why, it just was. Waves of enemies spawned in and in a variety of types. I, a Level 25 was taking out enemies of the same level with my sniper rifle, but equipped assault rifles and rocket launching shotguns to aid my destruction.
Once done, I fought a boss robot who was a Constructer who could MAKE other robots and spawned them, so taking him out posthaste was imperative. Then I had to option to make our robot we escorted dance, then he blew up. An even bigger robot came out, but the demo faded to a close.
Borderlands 2 looks better, plays better, and the quest structure seems to be a lot better, even with it being an escort mission I found myself having fun because the weapons and their variety were so rewarding to play with.