the dmc4 settings seen so far are no way worse than some of dmc3's. mission 14-18 were terrible, the level design was just atrocious. and besides, the levels looked too much alike, and while that did make sense to help set up the mood - especially in dmc1 - it's better to have more variety.
dmc4 may not be as good as the other 2, but that'd because of the gameplay, not the story or the setting.
and you can't beat dmc1/3 with the guns, if that's what you're implying.