I never watched the show when it was in primetime but I've been watching reruns now that its in a time slot where I sit in front of the TV. I like the show and I think its written well. I've always wondered if Charlie had a hand in casting because every hot A, B, C, D, list actress has been on the show.
It really sucks to lose Charlie but I think the new show did an adequate job of writing him out. I'm willing to give Ashton a chance to try and fill the void and let the show go in a slightly different direction. It probably won't be as good but still worth watching.
I'm more concerned with the kid character. Catching up with reruns its easy to see the kid was much funnier the younger he was. I don't see him adding as much to the household dynamic as he did in earlier episodes. Perhaps they could send him off to college and write in a kid from Ashton't past.
I'd say the show has already peaked but they just might get by with enough to make it salvageable.