Jonathan Frakes seemed to have problems with physical maitnence (especially weight) even when the show was going on, so it doesn't surprise me. I can't criticize though given what I turned out like.
That said Wil Wheaton *CAN* be blamed for Wesley Crusher to a great degree. See it's a hallmark of a good actor to sell a character and take what is relatively crap character and make it work, he failed to do that, and what's more made people hate the character. There have been plenty of "superkids" and such in fiction that people wound up liking despite being very similar kinds of roles, which is why they tried to do it with Wesley. In many cases the problems with such "child stars" is that they can't really do much else and lose it when they get too old to play the kind of role that made them popular to begin with.
I think the problem can be summarized to an extent by Wil's own comments in asking his mom why his character needs to solve all these problems other characters in the show can't. Basically if he can't make himself believe in the role while he plays it, that right there is going to kill it, and says a lot about why Wesley didn't work, and was always a bit "off".
Of couse I think a lot of it was also admittedly the writing, even as a kid my problem with Wesley was that he was never meshed into the ship very well. The kid was supposed to be a super genius, but it was never played up to the point where I really felt that he should have been given the free reign on the ship he was compared to the other kids in the family sections and such (and honestly that was a bit stupid). Had they played up the prodigy aspect or had him develop powers earlier on, it might have worked a bit better, but for any of that to work you would have needed to have Wil play the role better, and make it his own in a way he never did.
To an extent ever since the initial annoucements about Wil being "special" I kind of expected something similar to his ascension. I kind of predicted what "Q" was all about (the potential of humanity to be as powerful) pretty early on from his statements, and thought that Wesley was going to be something closer to that next step. I was actually expecting him to fight Q at some point, but that never really happened.
At any rate, the best example I can point to off the top of my head of someone who pulled off a similar role without people hating it, was probably Zoe (the Sheriff's daughter) from "Eureka". I don't think the character was ever especially popular, but also wasn't reviled either, and it worked for what it was intended to do (including the genius reveal) because the actress seemed to get into the role and have fun with it, and also admittedly because the guys doing the show didn't bring it out to the forefront too often. When she was present there was usually a decent reason for it... unlike situations where you'd say have Wesley on the bridge or whatever and there wasn't really any justification for why that character would be anywhere near the bridge of a military ship... which is a writing issue, but Wil was never able to play the role well enough to get you to overlook it. Wil is the guy who played Wesley as an annoying twerp, I'm sure other actors would have played it differantly and done much better.