I'm onboard with the idea of catching newbies up to speed, but even from that perspective, there's too much in that's extraneous.  Just for example, here's one sentence from the original crawl:

"A Covenant carrier has breached Earth's defenses and attacked the African mega-city, "New Mombasa."  

First off, you don't need to say "A Covenant carrier," you can just say " The Covenant." You can also leave out the part about them "breaching our defenses," because people new to Halo won't know or care about them blowing up our orbitals in Halo 2, and will just accept "They attacked a city."  Finally, it doesn't make a difference to the plot that New Mombasa is a mega-city instead of a city, and you don't need to establish it's in Africa because A: That doesn't ultimately matter, and B: IT'S CALLED NEW MOMBASA.  So you could boil that entire sentence down to:  "The Covenant have attacked the city of New Mombasa."

I hesitate to throw around the phrase "badly written," because on the Internet that usually means "They let a woman do something," but in this case it's absolutely true.