Ebert has a point. It's not a perfect adaptation but it's trying harder than Scooby doo was. Also I think Roeper was uncomfortable with all the rat scenes. When rodents appeared in movies, he would freak out a little.
Personally, I was disappointed by the film. I was alienated because the majority of characters look and act nothing like their original counterparts. Bill Murray was a good choice for Garfield, but he could have used a better script.
Garfield was done mostly well. The other characters weren't. Why couldn't Odie or Nermal be animated too? I'd forgive the movie better if they fixed that.
Now, I have never been a fan of Garfield anyway - it stopped being funny, assuming it ever was, years ago - and the movies are truly terrible IMO. Bill Murray admitted that he signed on only because he originally thought the director was Ethan Coen. And I am sure he got stuck doing the second one per the contract he signed. Murray's voice works fine, I guess, but Lorenzo Music IS Garfield, and Murray just doesn't come close to that eff-you approach that Music provided the character.