Halo 2 only gets worse on Legendary with the jackal snipers. Good luck lmao. If you can make it through 1 and 2, then 3, 4, 5, Reach, and ODST are all a breeze. You can do it!!
I did beat Halo 3 in legendary and most of Halo 4 and Halo 2. But usually with the games I kinda get tired of trying to beat them in legendary. Halo 3 was so fun to play in every difficulty so that's why I finished it.