George Lopez is a funny man even without the sitcom. The first episodes I saw of this too often made jokes at the expense of his mom. As I have watched this more, there has been more & more variety. No one on the cast is really safe from his wit now.
It seems to me as this season has progressed that George is getting more comfortable with the family sitcom Dad role. At first he wasn't, but he is getting More & more into a groove. This makes both him & the shows progressively funnier. They had added a couple of characters for George to play off this year too. His wife's dad is getting more & more involved in the plot.
His mom is still there, but not as central as past seasons. I think it is prudent to say with George's sense of comic timing, & ABC's lack of good sitcoms, George Lopez has a good chance of being here on ABC long after George W. Bush.