Well, I just finished watching Firefly and quite enjoyed it, with only a few caveats.

Likes:
1. The characters were interesting and displayed some development as the series progressed.
2. The SFX were more than acceptable – better than some shows now (I’m thinking of Eureka in particular), which is especially remarkable given that Firefly was from 2002.  The only exception would be all the battle scenes from Malcolm and Zoe’s back-story.  For some reason, those felt really cheezy.
3. Some of the writing was downright excellent, with occasional one-liners that were laugh-out-loud funny.  I especially appreciated the way that “native” languages and colloquialisms were incorporated (mostly successfully) into the script.  Also, the writers somehow managed to use poor grammar to good effect.
4.  I liked the music in general (especially the unusual use of fiddles) but thought the theme song was a little tacky and unprofessional sounding.
5. The acting was quite good in general, with even some memorable performances from auxiliary characters, such as the bounty hunter in the last episode.
6.  I liked how the makers didn’t let the futuristic setting take over – instead of trying to make every aspect of the show feel futuristic, they kept it to a more familiar-but-different level.  For example, the kitchen in Serenity was very homey…but then you realise that it’s on a space ship.
7.  The season was very cohesive – there were references to the events of past episodes and the writers’ main goal didn’t seem to be to make episodes that would simply stand on their own.

Dislikes:
1. I passionately hated Kaylee and her stupid “romance” with stupid Simon.  Seriously – could she be any more obnoxious?  In fact, almost all of the sexual tension in Firefly seemed really cliche, predictable and poorly executed.
2. Serenity is hideous looking – possibly the ugliest space ship I have ever seen.  It looks like an arthritic, pot-bellied praying mantis.
3. I know that some will argue that the whole “space western” thing is what makes the show unique, but I think that, while fun, the western themes made the show unrespectable.  It felt like they were looking for something cheap and handy that would utilize an excess of western props –  a cop-out.
4.  At times, the cinematography was absolutely horrid.  In one scene in the first episode, I actually stopped and went back to see if my computer had glitched out or something, but no – the shoddy cuts and disorienting voice overs were built in.

In conclusion, my main reaction is surprise that this show was canceled.  It seems superior to many other popular scifi shows and, if it continued, I would watch it.