Marathon. Creepy, proper 3D aiming, shadows, clips/magazines for ammo, oxygen for breathing in air or underwater, proper physics, neat cyberpunk storyline....it's a shame that the first game (up until recently with Aleph One) was only for Mac, although I certainly did enjoy blasting aliens with my brother on a G3 machine and an old Quadra 650 Mac - this is pre-OSX gaming at its finest - thanks Dad!
Replacing the characterful MIDI soundtrack of the first game, the second has a pumping dance track when you start up, giving you the idea that you are out to cause some mayhem and ruination to the Phfor from the first game. Most of the music in game became sound effect-driven to add suspense, but this still added up to a great title and an absolute blast on Windows or PC.
As for the band themselves, as far as I can tell the name Power of Seven was a pseudonym for another band called Psykosonik, who made music comparable to the 2Unlimited dance/pop crowd at the time. I gather that the mention of seven hooks in to the running theme of using the number seven in the Marathon games as well - although you would be better off looking at a Marathon lore website for a better of idea.
Either way, Power of Seven's opening title track for both Durandal and Infinity set the tone nicely and ensure that wonderful pavlovian response of going toe to toe with some Phfor, armed only with double shotguns. Bring it on!