The only game that's widely considered "bad" by many that I myself actually like (quite a lot, in this case) would have to be Silver Surfer for the NES.
This game was actually bad enough to earn a review by the Angry Video Game Nerd, who stated that the game was so hard, it'd be easier to go outside in a thunderstorm and dodge the rain than beating this game. I took that as a challenge, so I played Silver Surfer on my NES emulator and actually found a game that, was unquestionably a brutally hard game, felt very well designed in terms of gameplay, looked nice and had decent music (even though there was a very limited number of in-game tracks.) I honestly liked this game quite a lot since the difficulty, whilst extreme, was never to the point of being unfair, and was never at any point caused by any flaws in the controls, coding or design - the only issue I can say I had with this game was the fact that you had to repeatedly tap the fire button in order to shoot a stream of bullets - holding the fire button down would only fire a single shot and then do nothing until you let go and pressed the button again. It's annoying, but not a major issue really.
It's definitely a game for a very niche audience - only gamers who love the hardest of hard games will find enjoyment out of this one, I'll admit, whereas anyone else will likely experience nothing but frustration after strings of very quick deaths. From a design perspective though, it's a very well-made game, very nice graphics for NES standards, and the immense difficulty I welcomed with open arms. Definitely an underrated game, since its good traits are often overlooked due to the "this game is too hard" label that tarnishes it.