I saw an interview on Howard Stern, Dushku was saying what happened, she got the part, took Whedon to lunch, probably worn something very very low cut and asked him to do the show because it needed him. Thats how he got on Dollhouse and it shows, because its a pile of **** with a hint of something half decent there and one/two good lines, but it was afaik probably quite close to going into production before he came onboard so wouldn't have had much of a say and thats why supposedly, the second season was supposed to be better because it had more Whedon imput, but a great writer trying to keep a crap show going wasn't going to create magic.
Likewise I don't really have high hopes for a couple film re-writes, with limited scope for change. I mean he can't go "i'll set Captain America in a Firefly type settings".
He's at his best with his own show from original concept to final production from what I've seen, being that anything he didn't come up with, hasn't been very good at all.
Likewise, a film is incredibly limited compared to around 15 hours of TV per series, obviously

The thing that made Buffy, Angle, Firefly so great was the characters, their changes, the different episodes, the dialogue and the comedy you get from having so many different situations for them to be funny in. A film has to be paced to within an inch of its life and is still limited as all hell, I didn't love Serenity, because it felt rushed, the snappy dialogue was there but incredibly limited, because it had to be. The story moved to fast and it felt a little bit like a cop out, it should have been a 2nd series continuing back story line across many episodes, gradually finding a way to find the memorys, the feds getting closer and closer throughout the series and a two parter finale to finish it off.
Then again, some guys have a few great idea's, then can't do anything fresh and good, some guys can go on writing fresh material forever.
The films may/may not be good, but I'm still hoping for a new series thats Whedon from start to finish.