Zombie 4

This game is sweet - make sure you've got a Java Runtime Environment installed. This is one of the few 3-D shooters available as a web game, and it doesn't disappoint. Okay, it's not Half Life 2, but it's got a simple charm and great gameplay. This was developed by a guy named John G in Processing (you can find him in the forums if you have suggestions for the next game), which is a fantastic environment to write Java games in because it makes Java graphics effortless; for anyone that has ever struggled with Swing/AWT, this is an awesome achievement, and it even does 3D! If you're interested in making web games, you should definitely check it out. It's more flexible than Flash, and as free open source software, the price is right!