How many levels in left for dead 2

There are no levels but there are campaigns. Theres 5 campaigns they are: Dead center, Dark carnival, Swamp fever, Hard rain and The parish. If you have the add on you can access the passing which is a 6th campaign where you meet the ld4 original survivers.
There is also a new campaign called the sacrifice where you get to play with the l4d1 survivors.