I finished today with a wizard soloing. Wizard feels like easy mode even in nightmare and is the same boring routine now. Wasting an entire room full seconds after entering the door is only fun for the first 100 times or so. I took wizard first as I thought there would be more tactics with the time bubble and stuff, but it's much easier to just spam blizzard and disintegrate, using chain lightning with the +arcane power passive skill. Use frost nova + meteor for elites and bosses. (A few bosses were made completely inneffetive with spamming the cooldown-less blizzard spell.)
Anyway I'm going to start a Witch Doctor now for multiplayer.
Also, the story is pretty lame and filled with plotholes. I agree about the loot system being jacked up also. Game is still really fun despite those flaws.