You know what you are getting with the mission impossible movies, action and lots of it. I personally prefer the first movie but none of the three are unwatchable by a long way.
The HD-DVD release comes on a total of four discs MI:1 and MI:2 on one disc and MI:3 on two.
As far as picture quality goes the more recent the films were made the better the quality. MI:3 is reference quality and comes with many many extras including a video commentary which is not included on the bluray version of the movie.
The quality of MI:1 is less impressive but is still well above any other release of the movie in picture quality.
Overall a great box set that gives lots of action and a great way to show off the HD-DVD format.