Halo 3, I believe, was the hardest to make custom games on so seeing big and fantastic maps was great. Halo Reach was easier but from my time I didn't see much besides remakes. Did like stepping stones though. Halo 4 should be easy to make custom games but always found a lack of some because barley any of my friends played Halo 4. Funny on how nearly all my friends played Halo 3 & Halo Reach custom games with each other.