This is Halo: Reach's first 15 minutes

[CoDeX]

I know but it's Halo... it's not meant to have a happy ending, except ODST, it's the only happy ending in the series... Halo had everyone but 7 or so people die, Halo 2 ends disappointing but no one major dies, Halo 3 has only the Arbiter and Admiral Hood as confirmed survivors, Wars had the Spirit of Fire floating in cryo sleep... This is a downer series

Only 7 or so people survived out the hundreds there.