There are actually a significant number of changes between Halo 1 and Halo 2. If you get into Halo 2 hardcore and then try to go play Halo 1 again you will be awful. Halo 1 seems so much more unbalanced after playing Halo 2 anyway. The pistol rocks everything and everyone. I will say that I did enjoy Halo 1 Campaign mode much more though.