Joss Whedon may not be the best writer in the world, but he can write some pretty funny stuff. Most of what made Buffy and FireFly so good were the one liners and the action. Hell, the single greatest episode of Buffy had almost no dialogue (Hush) with the second best episode being the musical (Once More, With Feeling).
Buffy had more to it than one-liners and action. Firefly not so much. A whole lot of bland characterization, with the show expecting you to love these characters while pushing how cool the show supposedly is. But all that was way better than Serenity. At least in the case of Serenity shit WAS unpopular -Serenity flopped at the box office, to my great delight.
But the problem is that Joss fans push the view that Joss IS in fact The Best Writer In The World. And they think his writing was the best on tv. I guess they never saw Oz or The Wire. Or the whole load of other shows that had better writing. Factors other than writing made Buffy the quality show it was. But Firefly didn't have anything to save it from the shallowness that Joss's work often falls into. Almost a cynical shallowness. That show DID get cancelled, something which I'm happy about. And Angel got cancelled too, which thrilled me even more. There was one good season of Angel, the first season, and then the quality dropped out and it got worse every season after that. The final season made the Star Wars prequels look good by comparison. It was like nobody was making an effort and by the end it looked to me amost like Joss was deliberately fucking it all up, kind of reminiscent of the prequels actually. I have Whedon issues as much as I have Lucas issues.
From what I and many others can figure, FireFly got canceled simply because Fox didn't really want it. That became obvious when the first episode, which wasn't the first episode, aired. Instead of introducing all the characters during a two hour pilot, we were treated to a one hour episode that assumed you already knew who everyone was. Even I was a bit confused after seeing a preview of the pilot at Comic-Con. So it's no wonder it got canceled. Serenity was the way it was because it was pretty much a one off deal that had to cram about a seasons worth of story into 2 hours. I actually liked Serenity aside from the fact that Joss seemed on the verge of slaughtering the crew by the end of the movie.
With Angel, according to some anyway, it was doing quite well when the plug was suddenly pulled. That's probably why the final season looked like crap to you. The plugged got pulled right in the middle, so of course they gave up trying. They were pretty much trying to wrap it all up by the end of the season. Most of what happened between season 1 and 5, to me, was Joss trying to write around what was going on in peoples lives. Kind of like when Seth Green left Buffy, unexpectedly, and then wanted to come back. I also think Joss had way to much on his plate at this time (he was doing Buffy, Angel, trying to finish Fray, and I believe FireFly was in the early stages as well).
Like I said, Buffy was good until after season 5 (the acting, writing, and the stories). The musical is pretty much the one gem that came out of season 6. Other than that, they had her fighting a god and a pretty stupid god at that. She had more trouble with demons in 5 seasons than she had with a god in one. Yes, the last two seasons of Buffy were pretty horrible from all standpoints.
I think his writing can be pretty good and funny in context and with the right deliveries (probably why I liked FireFly so much). The only issue I have with Whedon is that he uses the same actors in everything he does. It isn't necessarily a bad thing, but it ends up looking like a reunion of characters. I saw a bit of Dollhouse and immediately went "Hey, it's Fred from Angel!" I have no idea what character she plays on Dollhouse.
If you care about art, it's perfectly reasonable to wish the money and time and resources were going into making quality stuff rather than crap. And if you feel that way you're going to wish the bad shows would get cancelled and replaced with good shows. Not that I expect the bad shows to all get cancelled and replaced with good stuff, but every one that is is a door open for a chance at making a quality show.
And who exactly are you to say what's a good show and what's not? Personally, I can't stand Lost, which is why I don't watch it. But wishing it gets canceled? I don't think it's immoral, but it's lame. Talk about wasting time. It almost sounds like your idea of "quality stuff" is the exact opposite of what everyone wants. The only show I've ever wished would get canceled was Friends, but that had more to do with the actors becoming arrogant and the show becoming really really lame than anything else. Hell, they spent several episodes on Joey not asking Rachel to marry him. But it got ratings, so it continued. I notice that none of them, aside from Matthew Perry, have been in anything really phenominal since it got canceled.