Aside from burnout, I think you and your group are simply suffering from mismatched expectations. You want a tense combat-as-war type game, where everything is strange and dangerous and player tactics are more important than mechanics. Your players seem to prefer a lighter combat-as-sport type game, where things are familiar and straightforward and can be enjoyed without much stress. Neither style is inherently better, but preferring one and getting the other is certainly no fun. You need to take a break, then come back with a strange new setting, maybe even system*.



*Not M&M, though. Much as I love M&M and have used it for different genres, it's a superhero game at heart. It's meant for mowing down hordes of unthreatening mooks and brawling with equally-powerful foes; "tension" doesn't really enter into it so much.