Well, it took some time due to upcoming moving and QuakeCon, but I just beat Doom 3... All I really have to say is WOW... The ending was great! I will not give away anything and I will refrain from posting all the screen shots I took during all of it... But really, if you have yet to beat it, do so... You will really be happy with the way iD Software completed this game...
It all comes down to LOTS of running and using the soal cube... You RUN [not walk] and kill all the imps and such as they are coming out... After you kill five, use the cube against the main monster... Repeat... A lot...
Tip: Use the rocket launcher against the imps... One shot kills... That will help you build up your cube to hit the monster with... DONT try to shoot the monster... Not point in that... Just use the cube on him...