I've been playing this one off and on since it came out, but I went ahead and finished it today.
To be honest, this game's difficulty level is about three levels higher than either of the previous ones, whereas the actual gameplay isn't improved all that much from the second one. The addition of a town-building element just made the game tedious, rather than adding anything to it.
Story wise... a good beginning, some good moments in the center, and a last part that falls flat on its face. The final antagonist is too flat, and the last boss battle is fairly anticlimactic. I'll be blunt and say that the second game did a better job in terms of story. I honestly can't give this game a good rating.