Here is my overall impression of the film.

Hnnnggguuuuuuhhhh.
Here are some of my other thoughts about the film, but with more words.
1. Michael Fassbender and James McAvoy, two of my favourite British men ever, in the same film. It is still rather odd to see them as leading men in a summer blockbuster comic book movie, and part of my brain refuses to accept it. But still. Fassbender. McAvoy. Together. McBendering. Fassavoying. It's too much for a girl to take. Both of them are easily the backbone of the film, and carry the plot and the entire supporting cast effortlessly, while delivering fabulous individual performances and having mad, mad, mad, mad, mad, mad chemistry with each other. Acting-wise, totally solid.

2. Speaking of mad, mad, mad, mad ,mad chemistry, the gay subtext within the Charles Xavier- Erik Lensherr friendship (intentional, according to the screenwriters) stopped being subtext and became plain text about 12 seconds after the title card. Even James McAvoy in an interview expressed mock surprise that the two didn't simply get married by the end. I can attest to the fact that he's not exaggerating; the Erik/Charles slash fiction pretty much writes itself.

You see? I mean sure, there's a winged topless woman in front of them, but they are in bed together. As if the Internet needs any more encouragement than that.
3. The entire thing could have just been Michael Fassbender Wears Nice Suits And Kills Nazis While Speaking Four Languages And Doing Funny Things To My Ladyparts, and I would have been just as happy. Happier, in fact.
4. I'm still trying to figure out exactly what the plot was - it wasn't the strongest of storylines but it served its purpose, I suppose. Russians something something CIA something Cuban Missile Crisis something something mutants are DIFFERENT something something January Jones' boobs something. The important thing was that it didn't feel contrived or overly-hammed up, and more importantly, it was a heck of a lot of fun.
But most importantestly (this is now a real word, okay?), Michael Fassbender sexes sexily around the X-mansion, wearing a turtleneck. Of SEX.

5. The women in the movie aren't exactly portrayed in the best light. CIA agent Moira McTaggart is down to her bra and panties within seconds of the audience meeting her (but guys, those were her government-approved stripper club stakeout clothes, they were for WORK dammit), January Jones did nothing but walk around in tight suits with her chest hanging out. The mutant Angel chooses to join the "bad guys" almost as soon as her character is established, which means she had pretty much no lines or any development for the rest of the movie.And then there was that line about why women shouldn't be in the CIA. It's hard to tell if stuff like this was meant to reflect the rampant misogyny of the story's 1960s setting, or if it's just what it is - blatant sexism that's present in nearly all forms of modern media which goes unnoticed so much of the time. But let's forget about all that because here is Michael Fassbender in a suit again.

6. I have not seen a single episode of Mad Men, and therefore cannot comment on January Jones' acting in that show, but holy crap was she completely wooden and uncharismatic and unappealing as Emma Frost. She had a couple of pretty snarky lines that would have worked wonderfully if delivered well, but meh. But that's okay though, because while January Jones was not-acting, Michael Fassbender was providing enough intensity, complexity, vulnerability and charisma to run a nuclear power plant. If you could run a nuclear power plant on intensity, complexity, vulnerability and charisma, that is.

And on top of all that, he was also providing the HOT. Such selfless talent.
7. As Grace pointed out, the so-called villains in this instalment were one-dimensional, paper-thin and completely dispensable. Kevin Bacon's evil ex-Nazi character started off with promise but by the end had been reduced to the cartoonish "let's blow up the world" brand of super villain. His minions fared much much worse - they barely had any lines, and I don't think anyone so much as mentioned Riptide's name.
8. One-note bad guys aside, this film does a great job of fleshing out Magneto's character and origin story (cause let's face it, this is Michael Fassbender's movie and everyone else is there to be pretty wallpaper [except McAvoy, he co-owns this movie. And my heart]). Wait, what? Oh yes, this film does a great job of fleshing out Magneto's character and origin story in a way that made him somehow sympathetic and also not entirely evil/wrong. His Holocaust experiences and the way they shaped his future bitterness, anger, and his vengeful nature did not feel contrived or overdone in the slightest. And where the previous X-Mens seemed fairly contented to leave us with the Professor X = Bald and Good/Magneto = Caped and Bad dynamic, this one gives us more shades of grey, and spade upon spade of sexy.

Fassy darling, you seem to have forgotten your shoes. Don't worry though, I'll help you put them on, so you don't have to stop that intense-staring-into-the-vaguely-off-camera-distance thing you're doing so well there.
9. The focus is placed more on making it a character study of Erik Lensherr and Charles Xavier, and not so much on the flashy CGI or explosions. However, the special effects, when they did show up, were effective and suitably dignified with the proper dosage of badassitude. This scene with the missiles, for instance, was crazy hot.

I don't know how much it had to with the hundreds of phallic weapons dangling in the air right in front of him, or the fact that in this particular scene Michael Fassbender suddenly develops a very prominent Irish accent broad enough to drive several trucks through, but I wanted to bone him so hard at that moment, unflattering helmet or not.
10. I can't think of anything else to say, so here's some more Fassbender. It is a truly great man indeed, who can steal the boiling, frothing oceans of my lust away from James McAvoy.

Sweet Jesus help me.
In conclusion:
Fassbender.
Well okay, in all seriousness, X-Men : First Class, while it has its share of flaws, is a tremendous amount of fun, and in no way a waste of a couple of hours and fourteen bucks. It definitely surpasses it predecessors in terms of quality and storytelling (and hotness) and if any sequels are indeed planned, I for one will be looking forward to them. Also, Fassbender. All fangirl-style objectification aside, the man is a ridiculously good actor, and it's nice to see him (and McAvoy) get some major recognition from the masses, so people can cast him in more movies and I can go sit in dark cinemas and squeal (inwardly) for many years to come.
Excuse me while I just sit here and swoon a thousand times over.
Just a quick afterthought ; another thing that really bugged me was how Charles Xavier had to put two fingers to his temple to let us know every time he was using his mad mutant psychic skillz. Someone needs to come up with a new way for telepaths to do their telepathing, because way to be subtle, Captain Obvious.
After-afterthought : How is it that nobody in Hollywood has cottoned on to the undeniable truth that Fassbender needs to be the next James Bond? Because if he were, I would actually watch one of those damned movies. Many times. In a row. Also someone should appoint me as Head Boss Queen Leader of Hollywood because no one in that town knows what they're doing.

