A couple of days ago I finished the campaign in Halo 1. I played it in Heroic difficulty like I usually do and many parts gave me trouble to advance but it was extremely fun. I love this game. After finishing it, I immediately started with Halo 2 which has my favorite campaign from the original trilogy (yeah I'm serious).
I'm currently just beginning the mission where the Chief and the rest of the human forces land on the second Halo, after the first Arbiter mission. By the way, the "boss battle" with the heretic leader was a pain in the ass. There pretty much nowhere to get in cover and his shields are very strong, even for the Plasma Rifles and Carbines. Took me a few tries but I emerged victorious once again.
I'll keep going with Halo 2 during the week and if everything goes according to plan, I should be starting Halo 3 by Monday. I hope I have enough time to finish all five games before my trip and without rushing my runs through them at the same time.