It's a bit like the Star Wars series in that the main film is like the original SW, it works out to be very popular so they go back and make a prequel so you learn how the characters ended up how they are.
Does it work? Yeah I think so. It's a pretty good action flick with lots of special effects. The acting is pretty good from the main characters of Charles Xavier and Erik Lehnsherr and Kevin Bacon makes a good baddie. You also meet Mystique, the Beast (Kelsey Grammer's character in X3) and a handful of new characters too. And some of it is filmed here in Oxford

Some plot setup issues are glossed over but it doesn't stop the film from being entertaining. They also set it up nicely for a sequel or two for more mega bucks!