Well, after Led Zeppelin, Queen is my second favourite band of all time. Queen was actually the first proper rock 'n' roll band I got into. I heard my first Queen song (Seven Seas of Rhye) at the age 5 (in 1992).
As far as answering the question whether Queen is underrated or overrated, I would say their work in the 1970s (especially albums like Queen I, Queen II, Sheer Heart Attack, A Day At The Races and Jazz) are quite underrated. I love Queen (mostly for their work in the 70s!) because to me, what set them apart from other bands was the fact that they did the pretty crazy thing of combining rock and opera. With the kind of vocal abilities Freddie had in the 1970s and the fact that they were so flamboyant, made me think that listening to a Queen album is pretty much like going to a Pantomine and to a Rock concert at the same time. It is indeed the best of both worlds.
I heartily disagree with the person who said that Queen was more focussed on being flamboyant than actually creating music which was worth listening to. Go and listen to tracks like "Lily of The Valley", "In Lap of The Gods : Revisited", "Nevermore" and "White Queen : As It Began". Where's the flamboyancy there? And whatever anyone on this forum might say, Freddie Mercury is by far one of the best vocalists out there. I don't think anyone could in the 70s tackle those opera-based rock songs like he could, IMO! The man could do rock, opera (I mean real opera music) and tons of other stuff! A real versatile vocalist! I don't think anyone can beat Freddie in terms of his vocal abilities in the 70s!
Now, eventhough I am a Queen fan, that does not mean that I am a fan of all of their work. I was absolutely put-off by their work during the 80s. The 1980s was the decade during which Queen officially lost their individuality by completely abandoning their progressive rock tendencies and becoming this arena rock band. I think the saying "if you have seen one band, you have pretty much seen them all" applies to Queen's work during the 1980s. But I still like albums like "The Game" and "A Kind of Magic". And the 1990s album "Innuendo" is a master-piece in my opinion! Queen truly showed some great potential of making a comeback there but a sad turn of events unfortunately prevented them from doing so!
All in all, for me, Queen's 80s work remains overrated! It kept people away from exploring their work during the early 70s (1973, 1974, 1975 and 1976) and really getting a feel of what Queen TRULY sounded like! And as for "We Will Rock You", that song, just fuckin gets on my nerves! It's been beaten to death more number of times than "Stairway To Heaven"!
And I have to say that the major difference between bands like Queen and Led Zeppelin is the fact that Zep maintained their individuality and unique style till the very end! Queen on the other hand foolishly abandoned it during the 80s! Queen for me are also strategists in a way, because if it hadn't been for their change in music style in the 80s, they would have been forgotten a long time ago, I guess due to their excessive flamboyancy, campiness and possible lack of mass appeal!