Warning: Spoilers Ahead. Use Your Judgement.

BrooksMarlin and Cap'nSalty have expressed pretty well the plot and I share their general feelings about the movie; as action flicks go, X2 is pretty good. (I do, however, wonder how it managed to get a PG-13 rating; it was definitely more violent in all the ways that count than, say, The Matrix Reloaded, which got an R rating. IMHO, this is just another example of how skewed the movie rating system is. But I digress...)

That said, I'd like to point out some technical problems with the movie. I'm excluding those problems that it inherited from the comic book (e.g. the impossible mutation rate required for the mutants in the Marvel Universe to exist), since there's not a whole lot the writers or director could really do about those.

  • Cap'nSalty already pointed out the problem with the ending monologue about evolution. The one at the beginning is similarly flawed. In the beginning, you hear Xavier talking about whether mutants are "the next evolution of humanity or a different species", or something to that effect. This makes no sense at all. If 'mutants' emerged as a new line of humans (and the whole idea is fraught with its own problems, but I'm not going to address those since they're inherited from the comic), then of course they're the "next evolution" of humans, regardless of whether they become the rule or not. And if they're a different species, they wouldn't be able to reproduce with regular humans (which they can).
  • Jason Stryker has apparently had a full frontal lobotomy. In that case, there's no way he could project as intelligent and cogently emotional image as he did. (Not to mention that how he can even understand Colonel Stryker's commands is a complete mystery.)
  • Nightcrawler couldn't use his power to sneak up on people or eavesdrop. In the comic, his teleportation leaves behind a pungent smell of brimstone. It would be quite noticeable.
  • Also, he couldn't do something like what he did to save Rogue. His power doesn't affect the laws of physics; if Rogue was falling at 50 m/s, she would still be moving 50 m/s when he teleported her back into the plane, which would probably kill her.
  • Why would a bullet to Wolverine's forehead even knock him unconscious? Moreover, considering how little skin there is in front of your skull in that area, it's obvious that the bullet penetrated the bone. How can that be? His skull is reinforced with adamantium!
  • Why didn't the X-Men reveal to the President that Senator Kelly was dead and that Mystique was masquerading as him? This would certainly be in line with Xavier's thinking.

    And now, some easter eggs:

  • Did you notice the names as Mystique was looking through Stryker's files? It went by too fast for me to catch them all, but right above Magneto's entry is "LeBeau, Remy" - Gambit's real name.
  • The pro-mutant debater on TV - from the debate Laurio (the security guard) yells at the bartender to shut off - is Hank McCoy, or Beast. The anti-mutant debater is Sebastian Shaw, or (I believe) Black Tom, who in the comics has a hand in creating at least one generation of Sentinels (someone correct me if I'm wrong).
  • A scan of the credits reveals Kea Wong as Jubilee. This is curious, since at no point during the movie do you see a girl who looks like Jubilee or has powers like hers. Possibly the writers or director simply wanted to find someone to call that in case they decide to bring Jubilee in as a main character in the next movie. tetrisboy and fuzzy and blue both claim to remember hearing someone being called "Jubilee" in the movie, although they remember it at different times.
  • We also see a very young Siryn (Banshee's daughter) and Kitty Pryde (a.k.a. Sprite or Shadowcat). All part of the skewing of the comic's chronology...
  • Finally, as Cap'nSalty noted, T.H. White's novel The Once and Future King is referenced twice. The first time it's simply Magneto reading it. The second time, which I think is key, is when Xavier is distracted, seeming to sense something; one of the children asks if he's alright, and he says cryptically, "Yes, I think everything's going to be alright after all." (or words to that effect). Then he starts talking about the novel. Now, The Once and Future King is about King Arthur's death and later return. We are given several unsubtle hints that the next movie will be about the Phoenix Saga, which is about Jean Grey's death and rebirth as the powerful Phoenix entity. It seems likely to me this is supposed to be a hint to anyone who might be familiar with the novel but not with the X-Men comic. (It's possible the first time is a hint that Magneto would once again rise - i.e., break out of prison and continue his war on humanity - but that may be stretching it.)

    If you've noticed any other problems or interesting things to note in the movie, or any error in the above, feel free to /msg me about it.