I'm a huge fan of Kerberos - SotS, in its "complete" form, is one of my favorite games ever. And I'm confident that Fort Zombie will be a good game, if only for Kerberos' history with SotS.
Yes, the trailer is far from ideal. After the great intro trailer, seeing something like this trailer is disappointing. But it was quite obviously rushed (and made with less care then it should), unlike the previous trailer. As was already said, the frame rate problems do not represent the actual game.
As for graphics, this is a $10 game. You can't expect all the flare and shine of a $60 game. What matters, in the end, is gameplay - and, if I know Kerberos well, Fort Zombie has everything to be great on that aspect.
Call me a Kerberos fanboy if you want (and you may be right), but it will take more than a bad trailer to make me question the talent on Kerberos and their commitment to making great games. I'm definitely getting Fort Zombie, and hopefully we'll see a better trailer before release.