I bought H2 the other day and have been hesitant to put it in. I have HAlo1 and got about halfway thru it and never finished it. Im afraid that if I play HAlo 2 that Halo 1 will be spoiled for me.
Halo 2 is a continuation of the story so it might be harder for you to follow if you haven’t played through the original yet. If you don’t feel like playing 1, but still want to know the backstory, I posted this link a couple days ago: Halo 1 Story
I’d estimate that it takes about 8-10 hours to beat Halo 1.