Most films have a standard "bare-bones" (no-extras) dvd and a "special edition" dvd with all the extra features. The X-Men films are the same, in 2000, the original X-Men dvd was released with a normal set of extras but in 2001, the special edition was released (X-Men 1.5) containing all the extras that you could wish for. X-Men 2 had the same but both were released at the same time.
The difference between the 2 box sets is that this one (the one with the red top) contains the special edition dvds and the other one (the blue and silver one) has the bare-bones ones.
X-Men is the blockbuster that re-established comic-book movies as credible entertainment, part character drama, part super-hero epic. This is a very good film and any problems with it are solved by X-Men 2 (Director Bryan Singer said that the first movie is almost a prologue for what is to come) as X-Men often feels like it is just setting up the characters and basis for bigger adventures to follow.
X-Men 2 is the big one, the first half has the feel of a political drama/detective story which perfectly builds up to the superhero mutant action finale. There are some great scenes including a teleporter attack on the White House, a "coming out" scene which goes horribly wrong and a final fight between two mutants, both of whom can heal from any injury in seconds and who have metal claws built into their hands.
This is a worthwhile purchase for anyone who likes the films and is interested in how they were made. The Extras cannot be beaten (the menus are fun too, the movie disc menu of X-Men 2 is great)