Team Fortress 2 is perhaps the strangest shooter I have played but it is also a lot of fun. The multiplayer shooter I had played most recently online was Day of Defeat: Source which is good but has some annoyances, such as giving each player a minuscule amount of health and never allowing the player to gather any additional health. For the most part though it is a fairly balanced and entertaining shooter, especially after you have developed some skill and learned the maps.
Team Fortress 2 on the other hand allows you to rearm and collect health, two huge factors for making a shooter better by helping to keep you alive longer and thereby have more fun. Another big bonus from my point of view is that the maps are relatively simple to learn, unlike many other games. It also has more character classes than most games and those classes themselves are so creative and disparate that it's a great diversion to switch classes periodically and try different tactics. Even when you suck it is still a blast to play. This is due mainly to the awesomely ridiculous graphics and the huge range of weapon load-outs that are available. Definitely worth a try just to see the insane and cartoony gore effects.