Resident Evil: Outbreak Files 1 and 2:
I'm not going to lie: I'm a huge Resident Evil fan. But even if I wasn't, I could see myself really digging these games. For those who don't know, RE:O was the name of Capcom's foray into Resident Evil online. You could play as 1 of 8 different characters, who each had different stats, abilities, item space, etc. You could team up with up to 3 other people online to tackle a variety of scenarios Resident Evil style, do Boss rushes, time challenges, etc. And given the variety (and surprising balance) between all of the character types, and the different difficulties, I never found it to get old (especially when your team sucks and you end up finding yourself going it solo while your team-mates try to kill you as zombies

The games were hella fun and if the servers were still online, I know I'd still be going back for more. Reviewers unfortunately Found the lack of voice chat to be a problem (although I think it would have broken the atmosphere, and you still can talk to others with pre-set voice commands, although that can be a hassle sometimes admittedly), and pretty much gave it universal 7s. I blame the fact that PSN is a relatively weak online community for some of the failure as well. But the music was solid, story was well done, gameplay was unbelievably fun and usually pretty hectic, and there were tons of unlockables for replay value and online rankings. I wish it still had the servers up

Devil May Cry 2:
Just kidding. This game is terribad.
Chrono Cross:
Let's get this out of the way: Although technically a sequal to Chrono Trigger, it has very few tie ins to the original (you probably won't notice any if you don't go diggin into the obscurities); the combat system is different, You travel between 2 different dimensions instead of time and instead of focusing on the back stories of several specific characters they kind of just throw a hundred randoms in your face and say go. But if you actually take the time to play the game and pay attention, you realize it's actually pretty damn good. There are branching points to obtain the same goal, the storyline for the world kind of ties in subtly through tons of little pieces instead of the usual "I hear the king of that town across the ocean is actually a goblin" or some other blatant "go here" prod. But I found the combat system to be pretty awesome, and the ability to obtain a ton of different characters to add to the customizability of everything.
Don't get me wrong, it's definitely no Chrono Trigger (definitely one of the best games ever made period), but I think if you renamed the game, it would have been received a lot better than it was.
Any games you guys think of to be sorely under-rated?