well i have been playing for a while now and ive seen a fair few events. my favourite being the game count a few years back. you should consider makeing a new one like it that runs over a week or so. and every milestone (5,10,25,50,75,100) the player should be awarded an item or weopon. for example.

5- weopon pickup (7 days)
10- X2 (7 days)
25- certain weopen bomb X1
50- a perm secondry weopon
75- a perm sniper
100- a perm rifle

Or you could run an event where every day you log in and play at least 4 games you get an item. and the more days you play in a row the item gets beter every day for example.

day 1, Add Type C & D (7 days)
day 2, Pick up weople ( 7 days)
day 3, colour code + cross hair (7 days)
day 4, X2 + Double up (7 days)
day 5, 15k sp
day 6, 2 X 1pcs weopon bomb
day 7, perm weopen

Players who play the full 7 days in a row and plays at least 4 games will get gifts.