I just played through the story in mp mode with some friends which was the point of the game to me. However...
The online mode isn't really a problem. really, if it 'burps' it takes less than 15 seconds to get back online. Menu and char swaps are QUICK (well, compared to Final Fantasy and previous Diablos). Character rebuilds are handy and really, it's just more along the lines of you have a ton of skills and can choose what and when you want to use them, it's just hard to keep everything handy at once. I think it's a pretty nice system.
If you like Diablo-ish games, it's a lot of fun and isn't really a big deal. I could have done without the "Princess is in another castle" routine at the tail, but that's another story.