Sorry if this seems too descriptive, but I'm a major X-Men fan.
The plot itself was weird, since it didn't match any of the timelines. Why is Iceman being treated as a new character? He was one of the original five. Where's Beast? Why is Pyro attending Xavier's school? What happened to Angel? Why are Toad, Pyro, and Mystique present but not Blob? Why does Logan act like he's never met Sabretooth? Why does Mystique act like she's never seen Rouge? Why are we shown Rouge's parents? Why is James Marsden cast as Cyclops? Who made that decision?
The list of questions go on and on. Singer just decided to take characters and sploosh them together and make a movie. That's basically the concept.
Hugh Jackman as Wolverine- Best casting in the film. He was unknown at the time, and really ended up fitting the role. However, the whole thing where he'd never met Sabretooth before was kinda weak.
Patrick Stewart as Xavier- Another good casting job.
Ian McKellan as Magneto- I don't think he's strong enough. He looks really weak. He pulled off the role though, just hope he doesn't deteriorate later on.
Anna Paquin as Rogue- Poor casting choice. Too young. What's up with her thing for Iceman? Where's Gambit? Where's Colossus? Why doesn't she have a thing for one of those guys that she's famous for having a thing for?
Famke Jannsen as Jean Grey- Too old.
James Marsden as Cyclops- He's just not a good enough actor, I don't think. Luckily, he's not having to really act in this movie, so all is good.
Halle Berry as Storm- Of all the characters they decided to include, why Storm? Why not Gambit? Why not Beast? Storm has never really been a pivotal character, nothing really resulted from her. She's always been supporting.
Rebecca Romijn Stamos as Mystique- I guess she fits the role. Her makeup was perfect, IMHO.
Ray Park as Toad- Good job.
Tyler Mane as Sabretooth- See: Hugh's Wolvie.
Shawn Ashmore as Iceman- Shouldn't have been treated like a newbie.
Those are some thoughts.