It's fun, though I don't think it's a 90+ game.
My friend and I are playing through it, he's a commando and I'm a gunzerker. In Borderlands I played the hunter and I really miss that class, I don't think I really like the gunzerker that much and we're too far into the game for me to start another character.
The game has really weird difficulty spikes. Sometimes it's a blast, sometimes it's really frustrating. A lot of the time we only really survive because my friends turret belches rockets (which is awesome for him but I do A LOT). I think the thing that is getting both of us is we both feel like we never have a good gun, or if we do, it's really low level or isn't level appropriate for long. The guns also seem to have less elemental effects than last game, though I could just be imagining things.
Another frustrating thing are some of the quests. It's cool they try to be varied, but for instance last night we were doing the one where we had to mutate bugs. Every time we would try to inject a pod, the hunter would snipe it. In that same area, we were trying to find something for Tina (who is hilarious, Ash is awesome) and badass buzards kept spawning on us. We eventually retreated and then both mysteriously died. It turns out we were out of bounds but with everything going on we had no way of realizing it.
Overall we're having fun but we both liked Borderlands better. The game looks great, the writing is brilliant, and when the game is on it's fantastic, it's just all those other "not on" moments really bring it down.
