JPL (BTW, I just realize that's your initial!)
Anyway, my internet went nut yesterday and couldn't log in at all I was hoping to play some co-op. Then my son got Left4Dead for his birthday and we just have been playing on that. (Awesome fun game, eventhough FPS is usually not my cup of tea but co-op make it very enjoyable).
As for characters, yeah, certain class get stuck if you focus too much into one element because some boss have immunity. I don't know if you ran into a dragon yet but he is immune to fire so if your HE is fire focus might be in for a fight there also. I went with back up plan with my Sera and gave her dual wield as 2nd weapon since I notice the BFG don't work quite as well on flying creatures and when I get swamp.
Wait until you get to the last boss....