I beat it. My friend, AY, and I went through the entire game in 10 hours of game play and no, not at one time. And I will have to agree that they isn't an ending per se. More of a segway to more maybe. But as for game play and mood and all other things that you went through up until the end were friggin' awesome. Wow. I love the general sense that I am badass with one job. Savetheworld.
So where does that leave us. Well it leaves us with my theory of what they are going to do next. It is similar to crack model. Sell us on $50 worth of crack based on the first drug we were given (Halo) and then make it so that we NEED more. They created an ending the leaves us craving more. So those with Live! accounts will be able to download new single player levels for $5. Just a theory.
So, don't get Halo 2. It's too fun for its own good.