Don't let the reviews fool you, this is a fun game!
Most of my playtime has been co-op with my Son and we did beat it. Was some of the best co-op play we have had in a long time. I have yet to complete the game solo but am about 3/4 of the way there (and level 50 on my Champion).
I certainly die a lot out of co-op (Son was a Bio Engineer so I really notice the lack of healing now) but then again what fun would it be without a challenge?
Don't get caught up in the reviews, you should definitely check this game out if you enjoyed games like Diablo, Hellgate, etc. But be warned, you may get hooked as we have!
If I could change anything I would say add more areas (hopefully we can download some later) and maybe some minor healing type trinket for non-healing classes. Those and a small shared character vault would be nice.