Perfect Dark (N64), this poor little game arrived at the end of this poor doomed consoles lifespan and has always been extremely over-shadowed by it's younger more perky movie-tie-in sister Goldeneye as well as Sony's exciting new Playstation 2 console that was set to make every gamer live in peace and harmony due to how amazing it was with it's emotion engine.
Unless you were one of those fortunate enough to actually have an N64 with the 4MB Expansion Pack, then you'll never understand the sheer experience this game provided. It was a truely graphically stunning game... I mean holy shit it was just amazing what they pushed the N64 to be capable of. Real-Time Reflections, Depth-of-Field, Full Weather Effects, Motion Blur, etc, etc. Only the next generation (well current gen) games boast similar effects. Then there's the gameplay with some amazing elements like full skeletal animation, weapons that can be shot from peoples hands, AI that responded to their situation and how you were playing, witty come backs, physics based puzzles. Let's also not forget the option to view all of the cut-scenes as if the game was a movie after completing it, the co-operative story mode (play together with friends), the counter-operative story mode (play against friends) as well as the multiplayer with BOTS. The only other game to feature bots to play against at the time was Unreal Tournament released a matter of months before. Certainly was the first time for a Console title.
To me it really is the most under-appreciated title on a very under-appreciated console.
Well with perhaps the exception of my next mention.
Elite
I'm not talking the remake on the PC 5years later, or such but the original BBC Micro wireframe only 1983 release. Most people know don't even know what game this is, many haven't experienced the sheer genius that is this game.
There is no storyline
There are no objectives
There are no missions
There are no goals
All you have is a ship, 100cr.. and an entire galaxy with 150,000 systems to explore, fight and trade between. Aside from it being not only a huge achievement but the first EVER 3D game, the game itself introduced what would later become RPG elements that had absolutely no bareing at all on your character physically leveling up. There was a full and adaptive economy system, based on the trade route you established. It was stragetic, action packed, and was frankly a truely one of those games that no matter how much it pisses you off; you wouldn't quite playing it and you wouldn't turn it off. Hell you couldn't cause there was no save feature!
It had a loading time a little on the uncomfortable side of 10minutes but once you're past that; it was a true gem that moved on to provide the basis for a huge number of space based games to come. None have ever truely matched it let alone surpass it.
The last underappreciated game I want to mention, I'll bet many here haven't even heard of let alone played. It was a budget title for the Amiga 500+ called Sqweek, and by all accounts it was a fairly basic game. Take your little fuzzball creature and turn all of the blue tiles to pink by stepping on them within a time limit. It was a fun, infuriating and all-round kick-ass game that was cool to just casually kick back and watch as the game let you get so close to completing a level before snatching the win away at the last second.