You can choose between 5 modes: Coop, FFA, Hardcore, Team Battle, 2v2v2. Where you then can vote between 2 maps. If on Splitscreen online, both players will vote on the same map.
Really.... well in Reach you can customize Amor/Emblems, Forge 2.0, which allows you to make maps from literally anything you cant think of, to the point of where weapons and vehicles spawn, to what gametypes, are playable on that map,
Speaking of Gametype, Reach has more diversity from: Slayer, Team Slayer, Big Team Battle, Two Vs. Two slayer, Six Teams of Two, FFA, CTF, Assault, Firefight/Co-op FireFight, Zombies, Racing, Team Snipers, Co-op Campaign, Griffball(User-Created Gametype that became extreamly popular in Halo 3),
Not only that, there's also a User Created-Map Playlist called, Community Slayer, that keeps maps in the fresh zone, and they're pretty unique,
Uncharted is a good game, but there's no way it has more customization than Reach, Period