Developed for the WOWIE Game Jam, SVANTE is a fast-paced wave shooter set in a small arena. Each wave consists of you battling five enemies, with a different weapon each time. The game starts you off with an assault rifle, but soon you'll be "downgrading" to double-barrelled shotguns, Desert Eagles and more.
SVANTE is pretty basic at its core, but it's good fun. If you're looking for a browser-based FPS to kill some time with, there are much worse choices than Affax's WOWIE entry.