Steve Martin stopped being funny around 1990. He is GREAT in this movie though. No one else could have done it the same. I've seen this movie about 5 times now and still laugh out loud.
The whole thing with the sniper especially was hilarious.
Sniper: Die, you random son of a bitch.
[Sniper keeps missing Navin and hitting cans of motor oil]
Navin: He hates these cans! Stay away from the cans!