VMars actually does have a big (though not huge) following. On the interenet at any rate, same with Firefly. What worked for Firefly, in my humble opinion, are the absolutely rabid, fanatical Joss Whedon fans. Some people went to see Serenity multiple times, just to show that they love Joss and his ideas, and I'm sure a lot of them loved Firefly too. Joss seemed to have had approx. 58 gabillion people worshipping him and everything he does, whether it's his comics work or his TV work, or god knows what else. (Obviously I am not in the "Joss is God" camp.) Rob Thomas doesn't have the same thing going for him, nor do I think he ever will.
Joss himself enjoyed VM because it was clever and fun, which is why I thoroughly enjoyed the first two seasons of Buffy, and the first two seasons of VM, too. But I don't think the 3rd season of VM was all that good up until last week's episode. As for Firefly's first season, I watched one episode and wasn't interested to even watch another one... at any timeslot. I own Firefly (because of the hype), Serenity (because it's a good movie), all seven seasons of Buffy (thank god for Costco), and the first two seasons of Veronica Mars, I can tell you the first thing I'd watch if given a choice from all of those. Veronica Mars.
There seems to be a lot of backlash against VM and a lot of "rah rah" for Firefly. I think VM is easy for people to dislike, since it's not everyone's thing. And the constant "VM RULES!" that comes from some folks on the internet can get grating, I'm sure. But what gets on my nerves is this: Firefly and Serenity aren't amazing, groundbreaking, wonderful works of art. They are NOT the best thing since sliced bread. I would really, really love to know how many people loved Firefly and Serenity without knowing who Joss is or having any other contact with anything else he did.
So yeah, I see why Serenity was made, and why VM won't be made into a movie. They really do not share the same kind of fans. But I hate to see people belittle the quality (or fans) of Veronica Mars. Even with meager support from its network(s), VM went three seasons. Sure, Firefly's fans got a movie. But they didn't even get a full season of episodes on network TV. I'm glad for the little Veronica that could. I don't think a movie could even begin to convey the awesomeness that was VM at its peak.
As far as the last episode of VM goes... It was nice to see Wallace flying something on the beach again... and Logan being there, too. Isn't that rather like the first episode? No car demolition this time, though. Very nice, full circle. Starting with Dick's rant towards his father a few episodes ago, the third season started to really get enjoyable for me. There, decent character development, I love it! Something deep and emotional coming through! With the last few episodes, it just felt like the show was getting back on track. More Weevil, more Wallace, more people I care about, more mystery and intrigue that's actually interesting, love it! I think the downfall of this season was trying to appeal to new people, getting new viewers. I didn't care for the minimizing of older characters, nor did I care for the new characters. I knew there would be new characters- she was going to college after all- but Piz and Parker were snoozefests. I'm not sure how I feel about Vinnie running for sheriff, but that storyline could have ended up really cool. Am I the only one who is curious about Duncan and Lilly (or is it Lily)? That is what he named the kid, right? The Castle storyline could have gotten super interesting, too. And I hate that the show did leave on such a bad note- I hate it when Veronica is such a shit to her dad. I loved the single dad/great father-daughter relationship Keith and Veronica had going on. I think the show ended doing what it did best- making you want to watch it to find out what was going to happen next.