It's in third person and levels are not exactlly like tracks, though you usually get rewarded for doing things fast.

Oh oh I have to mention this game. The author doesn't get enough credit for such a brilliant game:
http://www.inventivedingo.com/
It's as simple as Tic Tac Toe, but as complex as Chess.

I am in complete agreement. It's the first RPG I've every played all the way through, and how about that awesome cinematic ending?? Hollywood, step aside!

– Success?
– Smash it!
– I knew it would work!

Some of the most satisfying immersion of being in real horse combat ever made. I have been playing this one for something like 5 years. When I first started only one town (zendar) had graphics! This was before river pirates were added! Anyone remember Dark Knights?
I still play it now, on my original serial, but I have got the point where I can get up and seriously running in two nights with my own castle etc. The rest of the game, the missions etc, is not well balanced and a bit hit and miss. I only know one guy who went all the way to 50 and he cheated to make a Balanced Sword of War one handed.
The multi player looks awesome.

Cryostasis (Found here). Its return to classic survival horror. With fantastic settings, and the story itself is decent.
Pros
You're sent aboard a ship stranded in the ice. The ship itself is huge and the ambient makes the frozen mausoleum deeply immersive. Its extremely cold so you have to find heat sources aboard to keep yourself alive.
Plus theres a specefic feture thats just... great.
The Mental Echo is Alexander Nestorov’s ability to physically change the present by travelling back in time and altering the memories of crew members or even creatures on board the ship.
Alexander can only use the Mental Echo on those who died under horrible circumstances or those who lost the fight against the freezing temperatures on board the North Wind. As well as their bodies becoming frozen, their memories are frozen too; forcing them to relive their terrible deaths over and over again. Until they themselves become a source of the cold that’s crippling the ship.
Talking about immersion, the monsters are very creative. None of those wannabe silent hill or resident evil (4) wannabe monsters. They are very original and if i dare say it, frightening.
Cons.
The battle system is broken. Like riding a bike in front of a train broken. Okay not that bad, but the rest of the game just barely compensates for it.
Also sometimes you will find yourself wandering around outside the ship, slowly getting stiffer and closer to death. Sure heat source ARE plenty make no mistake. But they are placed at certain locations... being where YOU never are. (or maybe i am just horrible at looking?)
If you can get your hands on this jewel, do it! Its just original piss-in-pants fu

Another shout out here for Rogue Trooper. Brilliant game, very like Gears Of War.
Also agree with Audiosurf.
If you want mindless shooting fun then try Bullet Candy on Impulse. It's like Asteroids crossed with Robotron.
Psi-Ops: The Mindgate Conspiracy was a lot of fun, try that out if you liked Second Sight.
Finally, probably not underrated but I also never see people shouting about it. Chronicles of Riddick: Assault on Dark Athena. It's not much more than an expansion pack but considering you get Escape from Butcher Bay included and upgraded its a very good deal.

I *love* Battlezone and recently reinstalled both of them. First person RTS/shooter. The game still looks great, as does the sequel. Runs beautifully on a netbook too. Brilliant games.

Exodus from the Earth is a surprisingly good game despite what all the reviews say. It's is challenging on hard yet it's not to crazy except for one small level. It is very good graphically, and it has a nice Sci-fi atmosphere without getting to crazy. There is plenty of interactivity in the environment compared to most FPS games like you literally move an in game mouse to click a button on an in game monitor. Kind of like Sin, and No one live for ever. It is interesting finding out about the story as even though it is not epic, it's interesting to know about the world. The AI is preety good as they will throw grenades at you when your behind cover and they will try to flank and surround you. They will split of from each other and lay down suppressive fire at you. It is mostly noticeable in the more open environments though. Overall though I'm enjoying despite looked down upon it is.