The show is consistent.

SpongeBob has changed since the movie, but those changes have been relatively small in comparision to what happened with Rugrats. The only real changes are that SpongeBob's voice is a little higher, he's drawn a little more rectangular than he already was, some of the background characters are more caricatured, and the comedic timing is a bit faster.

The show is currently without some of its original talents, most of whom are now working on Camp Lazlo. But unless the producers do something terribly retarded to ruin the show, like add a new character who doesn't have anything to contribute, SpongeBob will survive.