Portal is a first-person puzzle game with a really evil sense of humor. I have read that it's supposed to be set in the same universe as Half-Life, but it seems a lot less grim in tone than that series. (Don't get me wrong, it's brutal, but it seems less so because you laugh pretty often.)
You play a test subject for a company called "Aperture Technologies" in what is basically a first-person shooter without any shooting (by you). Using a unique device that can create matching pairs of hole-like "portals." When you (or anything else, really) step, jump, or fall through one portal, you come out of the other one, which leads to some really bizarre situations which you kind of have to see to understand.
It's presented as a series of levels designed to test you and the portal device to destruction, but that dire scenario is somewhat lightened by truly odd announcements and encouragement from the complex's slightly deranged control computer. Messages like this, delivered in a cheery (if somewhat mental) woman's voice, made me laugh out loud while playing:
The next test includes an element of negative reinforcement. Please be aware that touching the floor in this area will result in a failing score. Followed by death.The puzzles are challenging, but so far solvable (and I'm not really all that good at stuff like this, so it might be a bit too easy for some), and the game is really just a fun experience.
Team Fortress 2, on the other hand, involves a great deal of shooting. And explosions. And knives.
Unlike Portal, which is a "simple yet hard-to-describe" solo thinking game, TF2 is multiplayer-only, complicated, and frenetic, to say the least. That's not to imply that TF2 isn't a thinking game, though.
In TF2, you are a member of a ... well, a team, obviously. You can play one of many roles on that team, however: heavy weapons, demolitions, sniper, spy, medic, pyrotechnician (A.K.A. flamethrower guy), engineer, scout, or soldier. Each role has a unique style of play, and a team generally needs a good variety of roles represented to succeed.
Most of the scenarios involve facing off against another team in a battle to control certain locations, either taking and holding territory, assaulting defended positions, or defending against assault. It's very fast-paced and violent, but, like Portal, TF2 has a unique sense of humor that really works.
The character archetypes each have their own voices and personality, and the game has many moments that sort of blur between action movie standards and professional sports. For instance, when you die (as you do very, very often), the camera zooms in on a freeze-frame of the enemy who did the deed, complete with dramatic music and the offer to take a screenshot for posterity.
When someone takes you out several times in a row, the game makes note of that fact, declaring them your "nemesis" of the moment, and, if they continue to kick your ass, it starts letting everybody know. This can be a little irritating if you're really getting shut down, but I think on balance it is a good thing for one reason: it makes it unnecessary for other players to do a lot of their own taunting, saving you from hearing "pwnt!" and other standards of FPS braggadocio over and over again from semi-literate twitch gamers. Believe me, that is a net positive.
The bottom line is that TF2 is fun as hell, and really well designed. I had a lot of fun with almost every class (though I have yet to try engineer.) The spy was a bit too tricky for me to play without getting irritated, but I think it's one of the more demanding classes, skill-wise. My favorite by far were the sniper (for obvious reasons) and, surprisingly, the medic. This is probably because people are genuinely thankful when a medic comes to their aid. It lets them shine, keeps them alive in the face of enemy fire, and can really make a difference.
I'm going to have to try the third game in the box (Half-Life 2: Episode 2) soon, but I think Portal and TF2 are going to be getting a lot more attention first.