When my dh and I were facing divorce last summer, I was afraid of the whole 'Disneyland Dad' thing - and I know other couples dealing it. At one point, I threatened to make him move BACK in with the kids and let ME be the Disney parent! But... then I realized, my kids wouldn't be better off. The more responsible parent has to be the custodial parent. I had resigned myself to letting him be that guy.
In the end, we worked it out and have stayed together. But honestly, it's not that much different - it's all in the attitude. He has a job where he works nights, and leaves for work just before they come home from school. On his days off, he's 'too tired' to do anything with them. On weekends, during his 'off time' he's too tired. But if I give him the choice of working on projects at home, or taking the kids to the movie, he'll go to the movie with them. My bitterness creeps in once in awhile and says that the only difference with him here and gone are 1) I have access to his entire check and we don't have to pay for two residences 2) I don't get to date and 3) I don't get every other weekend 'off'. But that's unfair (and probably telling, at times).
Think of it this way, for THEIR sake (not his, not yours)... would you rather he does the fun stuff with them? Or would you rather they had to sit around and do nothing? It's tough, but part of choosing not to be/remain married to the father of your children is tough. (And yes, unless we're discussing rape, it's ALWAYS a choice - parenting choices begin AT conception)
The thing is, you've got to let it go. It's only eating you up inside. Don't allow the kids to pull the "but Dad says" on you... EVER! Remember, when they're with him, they're telling him, "But Mom says" too! My kids are 12 and 9 and make their own PB&J sandwiches because "Dad doesn't do it right"... "right" being the way I do.