Just got my first couple hours in with Wilhelm. My co-op buddy is playing Nisha.
Level 6 right now. I like how the game gives you the first ability sooner. At level 3 as opposed to level 5- game gets started MUCH quicker, and the intro isn't boring like it was in the previous game.
Wilhelm's ability is really fun, especially flexible because you no longer have that "Will I be wasting my ability if I only use it to take down these few guys?" issue, because he can recall his drones early and get refunded 50% of their remaining active time. Instantly makes it more strategic because you can call out your drones for sustained fighting, or just because you need a quick heal and distraction for the enemy.
Right now I'm gearing my skill tree towards making Wolf awesome. It looks like a good strategy would be to get the target-lock ability for Wolf, so you can weaken an enemy, and then call in Wolf to have him finish off a weakened enemy quicker, which gets his buff ability faster (more enemies he kills = longer duration, more damage). So ideally I'd be running a strategy where I spread out damage but never actually finishing off the weaker lunatics- then having a buffed-up Wolf attack the stronger badasses.
Writing is hilarious. Jack is awesome. Oxygen mechanics are great. No complaints so far, looking to be another great Borderlands game.