As someone who played and enjoyed the halo ce multiplayer for a year and half,i have some map and game mode suggestions which will help in deciding what game mode to choose for a particular map..i ll list some map info which i find to be quite fun and exciting
Blood Gulch:Blood Gulch is what de_dust is for CS.Kinda like a football feild,CTF is most played here.excellent map for race(underrated)
Chiron TL34-Smallest map,my fav,cemetery for noobs,quite puzzling map,best played with shotguns,alone.
Boarding action:A map in space/infinity with a deep hellhole in between
,good for CTF/Slayer.Snipers and Rockets are the best weapons here.
Battle Creek: Small map(cute),hard to kill if u get on castles,good for shotgun/rocket slayer match and king of the hill/CTF
Hang em High:Kinda like a big warehouse.CTF is good so is Slayer.All weapons do good here.Slayer with sniper is also fun.
Sidewinder:Quite a big map,CTF is best played here.Good for all weapons vehicles,turrets etc.Lots of sniping spots.
Danger Canyon: My favourite map.long,beautiful,good for CTF,Slayer with all weapons and vehicles.
Damnation:spawn campers' delight
good for CTF/Slayer.has a Dam or something with hellholes in between.
Rat Race:another spawn campers' delight area.medium map;good for king of the hill,slayer,CTF.
Death Island:a big open map which 'i dont GATE it !!'
CTF is the only mode i found to be fun,here.
Timberland: Greenish map with many small cliffs.best modes are CTF,King of the hill etc
Ice Feilds : Icy place like sidewinder,have a few sniping spots,all vehicles.CTF is good as well as Slayer.
Longest:mm not really as long as in the name,confined spaces,nader's dream as well as spawncampers',CTF,slayer,king of the hill.
Prisoner:Kinda like a three storied prison,small map, dont like CTF here.
Gephyrophobia:A station in space with deep hell holes in it,love the way map is designed
Good sniping spots.Banshees in the map=invinsible.CTF/Slayer
Delta ruins:Most underrated map,medium map,slayer is good
There are also some other maps like infinity/direlict which i didnt have played much.Also i rarely played oddball mode so couldnt add any info.