Perhaps Race Against Time isn't as exciting as the other Ben 10 films because it is a Prequel and you don't get far, but I wouldn't call it a bad movie. All the animations are really good. It depends which order you see the movies in.
I mean, if you left Race Against Time until last, when you had already been on the edge of your seat seeing whether Ben would save the solar system at the end of Secret of the Omnitrix, you might feel a bit disappointed, But if you saw it first, I am sure you would enjoy it and be keen to see the rest of the series.