I kind of like it. In fact, a part of me likes it better than the NuEnterprise because it's basically a new design, even though it has all the familiar shape primitives and configurations. The Enterprise itself, in my own personal aesthetic, has deviated too much from the original design and in too many odd ways (curved pylons, bulbous nacelles w/ blue bussards, absurdly huge size, brewery, etc). Vengeance is a nasty looking thing, but as you say, it was built for combat and nothing else. I personally think it works. It isn't the Enterprise, so anything can be done to it as required by the plot.
I think a lot of folks don't like it due to the political aspects within Starfleet that it represents in the post-Roddenberry multiverse. It is Section 31's hotrod, for lack of a better term. Many Roddenberry loyalists vilify DS9 in general and S31 in particular for egregiously deviating from the Great Bird's "vision" of the future (for the same reason that I think DS9 is the best Trek series since TOS). It's a psychosomatic response, not to ugliness of the design, but rather to how far the ideal has fallen from Utopian principles, symbolic of the "ugliness" that has permeated Trek and its alter ego of the Federation.
Then again, maybe I'm just talking out of my ass.