1) It was solid. I do not think it was on anything like Avengers level as some are saying, or Captain America 2 level which is likewise up there. It wasn't as clever of a script and wasn't as neatly tied together plot wise. It did however bring together most of the different pieces well for what it was. I'd still put X-2 as the best X-Men movie. It was cleaner and much simpler and still holds up as one of the best comic book films period. This was good, but not great.
1a) They went back to the DNA intro for the credits too. I approve.
2) X-3 appears, somewhat correctly, to be virtually ignored in canon other than one critical scene (Jean, which has come up twice now). It was rather crucial from that movie that the viewing public kind of knows coming into this one "oh yeah, uhm, Professor X, he's not dead. And Magneto still has his powers". Because they really only get that from a stinger scene at the end of a bad X-Men movie (the aforementioned third one) so the public is liable to be somewhat confused as to why these characters are alive and kicking since not everyone watched it or saw the stinger sequence.
Even with that rather important detail involved, it does seem pretty clear X-3 is just a bit of trash thrown off the side whenever possible.
3) They did do a pretty quick job introducing the new characters and had a good deal of fun with the powers. Bishop, Blink, Quicksilver in particular (plus Storm and Magneto get some fun bits). Sunspot and Warpath are basically introduced, but not even named that I remember (Blink wasn't named but seemed busier and more helpful). Which is fine really as we're mostly exploring Mystique/Magneto/X triangle with Wolverine around but the previous X1-X2 films had a lot of attention for Rogue, Storm, Jean, or Iceman as more full characters alongside the main lines. There wasn't much of that here, really zero character development occurs outside of X and Mystique.
4) Quicksilver is probably the only funny part of the movie. Which is an issue as Wolverine is usually funny and comic books (other than Batman) lend themselves to be somewhat humorous. I don't think there was much humor. The last one had some more bits of references here and there and funny routines that helped it along with the weaker characters. This has maybe a couple of funny routines involving Wolverine (not setting off a metal detector).
5) Lawrence makes a much better Mystique than Romijn. But she might just be given more to work with. Really other than the X-Magneto dynamic and Wolverine, she's the most interesting character in the films but they hadn't explored why that was until these new ones. Because she's the only character who stands in the middle pulled between the two main characters and their polar opposite views. Like a Catwoman to Batman routine. Everyone else has a pretty clear stance, even Wolverine. She has a more mysterious and mixed stance, especially in these last two films. Someone who can be anyone in the world has a very unusual role in philosophical and ethical terms and it's really only referenced once in the first films as a motivating factor (the second one when she talks to Nightcrawler). It's getting a lot more airtime now.
6) I realize Shadowcat has that power in the comic that the film is based on... but it might be nice to know when it shows up or why in the film. It's just kind of there. They explain what it is she's doing, but there's no explanation where it comes from. There's a stretch there from "a little girl who can walk through walls" to "woman who can send people's consciousness back into time".
7) They rather conveniently eliminated the bulk of the more annoying or useless characters from the last film. Which was most of them. There's a couple cameos, but Beast and Mystique are the only side characters from that group I'd prefer to keep seeing around and that they developed enough to keep around.
8) The stinger at the end is promising. I'll be curious how that plays out.