I'm finding most of the game's later bosses, I'm talking post game raid bosses to pretty be impossible in Solo without using some of the broken combinations, even at level 50 with a spec that is pretty powerful, these guys just wreck, which they should be difficult as they are harder then final boss difficulty, but they should at least be possible solo.
I know, maybe I just suck at the game and I know it's not meant to be played alone, but I'd like to see it be more of an option.
The only raid boss that I truly dislike is Master Gee. Even though he can be defeated pretty easily with specific weapons I just don't think he is an interesting fight. I do find it somewhat amusing to run in his acid pool while using one of moxxi's health regen weapons though.