I think what makes Monroe a great character is that at first he just seems like a stupid little kid, but then he shows his full potential when you least expect it. He lead the angry mob against Krabs in Krabby Land, he called Krabs a cheap tightwad in Born Again Krabs, and I think he lead the mob against Spongebob in The Sponge Who Can Fly.
However, I didn't like his role in Hocus Pocus. He's just depicted as a stereotypical spoiled brat, which is OOC even for a character as minor as Monroe.
It would be nice if he appeared in more episodes (and got his name back, Timmy just isn't as good a name).