I've been totally hooked on Battlefield 2, the new squad FPS. It's got great teamplay, aided in part by built-in voice over IP so you can talk to your teammates.
But adjusting the microphone so the gain is correct is a total pain. In addition to the in-game settings I've found at least three different audio control panels in Windows that affect it. The key is to ignore all of Creative's crap software, go to Settings / Control Panel / Sounds and Audio Devices, click the Voice tab, go to the Voice recording panel, click Volume, then boost the Microphone slider. If you click Advanced you can also set a +20dB boost which helps too. Basically turn up the gain in every setting in Windows, then use the in-game control (with feedback) to lower it back to a reasonable setting.
I bet this isn't so hard on MacOS.