A game isn't overrated just because a few people don't like the game. The only games that are overrated are games that score more than it deserves because of hype. But when there's a universal mark of approval from gamers, apart from a select few, it certainly isn't overrated.
I also don't believe that subjectivity is all that matters when judging games. There's some degree of opinion, but I believe a game CAN be objectively good or bad. If this wasn't the case, try one of the budget games from Phoenix on the PS2 - can you honestly say these games aren't objectively bad games? Some very few people may find some enjoyment in them, but some people also find enjoyment in being burned by cigarette stumps. I guess that could be said to be underrated?