K so these are some idea's i think would be enjoyable for the game and that would make user's want to come play over and over again, if you dont like it just reply on how it would be better and what not.
Daily tournaments- for ex. at every day like at 5pm or you can have 2 for diffrent timezone's and it would be the casual 1 on 1 fight but it can be diffrent gamtypes like for ex. first blood which would be the first who would get hit. it wouldnt be fun if the same guy wins every tournament because he trains more, it would be better if the newbs can win once in awhile :]
CTF- well im pretty sure you know what this means
KOTH- 2 teams would face eachother to see who controls the hill, the longer your teams is in the hill the more points you add up and the first to 100 wins.
Survival- players would be spawned into an arena with npc's trying to kill them and the players could kill eachother. The last man standing wins.
Umm thats all i can think of so just reply what you think