Decent.
I did watch the 'Lizzie McGuire' television show when I was younger, not religiously or anything close but I do remember liking it. I wouldn't, though, know if it works well with the exact storyline, given this film connects to what occurs on the small screen; I was an on/off watcher at best.
Hilary Duff (Lizzie) and Adam Lamberg (Gordo) work together nicely, but it's a slight shame that Lalaine (Miranda) doesn't appear - I recall liking her in the show. Elsewhere, Alex Borstein (Ungermeyer) and Yani Gellman (Paolo) are solid.
This is nothing overly memorable, and it isn't far ahead from being a bad film; the ending drags out, especially the music performance. However, all in all, I'm satisfied after viewing 'The Lizzie McGuire Movie'.