Over the past couple days I've gotten in some multiplayer games of Dungeon Defenders. There are four classes in the game and there were four of us so we each took a different class. It turns out the game is much more tower defense than first person shooter and the 'best' class is the one with the best towers: the wizard. Snuggles is our wizard and he always gets the 'most valuable player' award at the end of a level because his turrets kill practically everything. Certainly all of the cannon fodder that exists solely to make single target damage dealers worthless all gets to die to his fireball towers.
That said, the game is pretty fun and the other classes do have things they can do to help win the fights. They just don't do the things that score points most efficiently so they never get to top the meters.
I'm playing a knight that most deals with being tough and building walls. One of the things that I noticed while playing a solo wizard is my towers kept dying so I had to put some of my stat points into tower health. In our little team Snuggles can pretty much ignore tower health and focus on the three tower damage stats. I ignore the three tower damage stats and just make my things tougher. So my stuff gets beat up and Snuggles' stuff kills things. It seems like a pretty good combo thus far.
Lino is an archer which doesn't seem to have turrets that can compete with wizard or knight turrets. What he does do is a high amount of single target damage. Most of the time this is pretty irrelevant (everything will just die to turrets anyway) but every now and then flying monsters or huge monsters or bosses will spawn and it's really useful to have a mobile ranged attacker who can take them out.
Robb is a monk that doesn't actually seem terribly useful. It's listed as being the most challenging class but I'm pretty sure that just means it isn't very good. Monks seem to mostly have buffs and debuffs that might actually multiply very well on hard difficulty levels to allow the specialists to do their things even better. But then I don't know what else he could do. Because the game is set up so anyone can upgrade/repair other people's stuff there's really no need to have more than one person building attacker towers. There's no need to have more than one person with a lot of points in tower health. I guess a second generic damage dealer is fine, and that's probably what monks actually do. (One of the constraints in the game is a limit on how many things you can build, and I don't know if building random auras is worth skipping out on more damage turrets.)
I am definitely enjoying the game. It has lots of little tricks to make you want to keep playing with levels and gear and scoreboards and such. Definitely a good inclusion in the bundle thing I bought.