As some of you might remember, Revelations 2 is my favourite RE of all times. It even managed to dethrone RE1 and 2, which I didn't think was possible before I played it, and my only real complaint is how they handled Claire (both her new voice and her new personality, or lack thereof), but that doesn't ruin the fun for me.
But is it underrated? Not sure. "Underrated" would imply that it doesn't get the recognition it deserves, and that just doesn't seem to be the case. According to
this poll I created shortly after the game's full release, the majority of the users here who voted clearly enjoyed it, and so far I haven't met a single person who didn't like it at all, even though it's not a numbered main title and wasn't made with the same resources.
I would say, though, that the Revelations series
in general is underrated, because despite how much everyone enjoyed the first or the second or both entries, I hardly see anyone asking for a Revelations 3. Besides me, that is, because I'm a lot more interested in the Revelations series than in a continuation of RE7.