I'm not sure if liking or thinking any of these games are good is unpopular. This is more games I really enjoyed that people didn't really talk about.
Army of TWO: The 40th Day - Not the strongest in the story or world building category, but an excellent co-op shooter with plenty of satisfying moments and great mechanics.
Disney's Castle of Illusion Starring Mickey Mouse (Remake) - This one was a bit of a quiet release for me. I stumbled upon it on XBLA, tried it, bought it, passed it, and loved it. It's a solid and great looking platformer with tons of Disney charm.
Prince of Persia: The Forgotten Sands - The original Prince of Persia received tons of praise and still gets acknowledged from time to time, meanwhile The Forgotten Sands is, well, forgotten. Which is a total shame as it does everything the original did and more, but better. It's a satisfying platformer with satisfying combat and creates so many unique obstacles that feel so rewarding to traverse through.
Sonic Lost World - This one does get trashed a lot by the Sonic community and I don't get it. The gameplay is solid and for the first time in a 3D Sonic game, you're in complete control. Sonic is slowed down significantly from the current boost formula but it works as good as it did in the Adventure games. You can actually run in perfect circles and run in straight lines without feeling like the level design or responsiveness is going to kill you. It's not a perfect game by any means, but it's not remotely terrible either. It may be messing with the formula again, but that's not necessarily a bad thing when the game is actually fun and well made. Honestly, Lost World should be the basis for future 3D Sonic games but unfortunately, that'll never happen now.
Spider-Man: Web of Shadows - If I recall correctly, this game wasn't exactly well liked by critics and not many people ever really spoke up about the game. Why? I honestly don't know. It was by far the most exhilarating open world Spider-Man game. Combat was amazing and diverse with Spider-Man being able to keep up combos in mid-air, kick ass while standing on the side of a building, and switch between his symbiote suit and classic suit on the fly, altering his attacks and boy are there tons of enemies in this game. By far the best open world Spider-Man experience.