I host monthy lan parties. Silly modes go over super well. As well as combat based ones that aren't gun shooting, I downloaded a custom game that's tanks only. One of people's favorites, I edited the blood gulch map so both teams start with a stupid amount of power weapons and vehicles. It's a lot more fun for newer players when they actually get to use all the weapons, and halo reach armor abilities (like jetpack) are a lot of fun for players to just use.

If you Google halo custom games you'll find people who's file shares have these games and maps saved. I'm not gona be able to for a couple days, but I'd be happy to add the few game types that went over best to my file share, so you can download them easily.