The concept is interesting; it's a "road" movie concerning fish in the south Pacific.
Nemo is the only survivor of a shark attack that swallowed his mom and all the rest of his siblings (considering that the shark got all the rest, that Nemo survived in the first place is a plot device, but we have to overlook that for the moment.) In consequence of that incident, we have a familiar character in this story, the "overprotective parent". Nemo, of course, is the stereotypical teen who thinks his parents are ruining his social life. So, when prodded by a clique he trails out of fish school, he swims out into the ocean and deliberately touches a boat against clear orders. He then gets swept up by a diver and taken away in the boat. Dad immediately begins swimming after said boat.
Now, fun parts of this film are generally focused and triggered by the blue fish Dory who happens to begin following Dad around mid-voyage. She's funny because she has a terrible case of memory loss, the running gag being that she has to be reminded every day who she is, who Marlin is, and where they're going. The second is that she won't stop chanting the boat owner's address (which they got off a set of goggles that were knocked overboard). The other fun moments are running into Crush the sea turtle and being picked up by a vegetarian sharks' club.
I guess, simply as a movie, the biggest problem one could have with it is that it is so slow. There are only so many times you can get a laugh out of having a character forget everything that just happened, but to my memory, (which is poor) that happens a lot in this film. On the other end, Nemo's attempts to escape the fish tank are a bit slow because there's only one thing they can do: jam the filter, which is supposed to cause them to wind up on the windowsill so they can escape.
I don't see anything objectionable in Finding Nemo. There probably isn't anything. Since this one was the most monetarily successful one made before Toy Story 3, the general public must have thought it worked.
"That French Food"
Sorry, I can't spell the title and I can barely remember the gist of the plot. Sometimes I forget this one was even made. Therefore I can't talk about it.
A Bug's Life
In our house, this one is regarded as the most boring one made. The story follows an ant who invented a machine to accelerate harvesting. After this machine causes chaos by breaking down and stalling the line, the innovative ant is banished from the colony. The main conflict, however, is that a horde of grasshoppers demand tribute from the ants. The tribute is delayed, so the grasshoppers begin a reign of terror. Meanwhile, the inventor is looking for warriors to fight off the grasshoppers. Eventually, he convinces a flea circus to follow him. These actors, of course, are totally inept at anything else.
Good: The climax is a fun scene. It's also fun to see that in the end, everyone is using the machine. the Grasshopper chief's luckless henchmen also provide some laughs.
Bad: In general, this movie simply isn't funny. See the first sentence above. I doubt that we could give you a specific reason why though. It just doesn't feel right.