The movie wasn't them at their best. It was simplified, greatly, for massed audiences.
There's countless episodes of the show that're far funnier.
Short of getting a hold of or buying the box sets (I'd reccomend the box-set with Time Chasers, Boggy Creek II and Touch of Satan on it. (Volume 5)
You may have to Amazon it.
If you're not willing to make that large of an investment, check out
this site where bootlegs of the episodes not on DVD can be purchased.
There's countless episoides in there that can be named that are far funnier than the movie was. "Final Sacrafice", "Riding With Death", plenty. Each DVD only costs around $3 so a much more disposable investment.
-This site has allowed me to bump up my collection from the retail DVDs to nearly now having the entire series so it's safe.
It should be noted the show has 3 eras. The Joel Era, The Mike Comedy Central Era and the Mike Sci-Fi era.
Joel started the series on "The Comedy Channel" (which became Comedy Central) after it was picked up from a Minnesota local station (KTMA season -which is.... rough) his humor tends to be a lot more whimsical and the Host Segments have a strong "Saturday Morning Kid's Show" feel to it. Mike picks up as host in mid-Season 5 and the whimsy is toned down quite a bit. The show left CC at the end of the truncated Season 7 when it was picked up by SciFi. Sci-Fi's years are much debated, and mostly it seems disliked, by fans. Mostly because the host segments are seen to be a lot lamer (new "Mads") and the movies have a lot less variety.
Personally, I quite like the Sci-Fi years.
Joel's humor as I said is a lot more whimsical and light, I think Mike's humor is much more sharper and biting -he also had a different relationship with the bots.
There's a handfull of episodes that're just terrible, but for the most part I'd think you'll get a good laugh out a great many of these episodes.
Good luck!