SOLVED Do I have to see the TV series before I see this?

The movie is designed to be self contained. Many have watched the movie and enjoyed it without being aware there even was a series.
That being said, you will get more out of the movie if you've watched the series. Mostly from being more familiar with the characters. But the movie is perfectly enjoyable without the series.

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Aliens? Us? Is this one of your Earth jokes?

You've probably watched it by now, but I'd recommend seeing the series first if possible.

Though it isn't 100% necessary, seeing the series first does add a lot of weight to the characters and backstory that makes the film feel more "complete."

And FURTHERMORE, this is my signature! SERIOUSLY! Did you think I was still talking about my point?

No, I watched the movie rented from Hollywood Video twice before the clerk told me there was a previous TV series.
I was shocked that I missed it but I was buying a house and working my ass off then with little time for Television.
Probably didn't even have cable back then.

However, that said, you would be missing a TON of great writing and acting by skipping the series.
Buy the DVD set and you will be watching them over and over for the rest of your life.

I watched it four years ago before watching Marvel's The Avengers, because I wanted to get a sense of how Joss Whedon was as a director. I knew his great rep as a screenwriter & how busy he had been with his TV shows (Buffy, Angel, Firefly), though I had never watched any of them. But I watched Serenity because it had a rep of being self contained, and it wasn't necessary to have watched Firefly first.

I came away with mixed feelings, and wishing absolutely I had watched Firefly first. That was my major complaint, feeling a bit lost. So yes, watch the series first; it's only 14 episodes.

(The movie itself falls a bit short on the cinematic side, but that's largely because Whedon was given less that half the budget a scifi epic needed and half the shooting schedule. But he made the best of it and went ahead, because this was his dream project and Universal made it happen.
It feels too much like TV in the first half, with the camera movement and staging of action, before Whedon finds his feet. The lighting is appropriately cinematic - thanks to veteran Clint Eastwood cinematographer Jack Green - and the story is very solid. But watch Firefly first!)

Everyone else may be an a**hole, but I'm not! - Harlan Ellison

I'd seen the film a couple of times (and enjoyed it) but now that I've watched the series, re-watching the film is not so fun anymore. Looks great with a much bigger budget but it's too dark and the plot isn't that interesting.

I saw the movie before I saw the show. I thoroughly enjoyed it. Years later I watched the show and loved that too. I have watched the movie since then and I can honestly say that I enjoy both the movie and the show.