Well…Fort Defense works.
Believe it or not, that's not damning the game with faint praise. Rather, it's meant to assuage the fears of anyone who took note of Fort Defense's European release issues, and was concerned that the game may have reached North America in a similarly unplayable state. Happily, if you're buying the game here, you don't have anything to worry about — it installs and plays without any problems.
Of course, if your standards for games are a little more demanding that simply asking, "Does it work?", then you might find Fort Defense to be a little wanting. Which isn't to say the game is a terrible trainwreck or anything; I've certainly played far, far worse games than this.
I've also played far, far better, though, and that's where the problem lies. Fort Defense is neither very good nor very bad; it's just there. It's a run-of-the-mill tower defense game that doesn't alter the formula in any significant way. Let me put it this way: the most significant change to the formula that Fort Defense makes is that it gives you the option of using a couple of non-stationary weapons, like diseases and reefs.
…Are you trembling with excitement yet? Me neither. Round that out with slightly terrible graphics and maps that all look very, very similar, and you can see why it's hard to get too enthused about Fort Defense.
I don't want to be too down on it, though. As uninspiring a run-of-the-mill tower defense game it may be, it's still possible for such games to go horribly wrong. Fort Defense obviously shouldn't be your first choice if your Vita's crying out for some tower defense — not when Pixeljunk Monsters and Plants vs. Zombies are both available — but if you've got a few dollars and that particular itch to scratch, then it won't be the worst purchase you've ever made.