We'll start with the most important thing you want to know, should you see it? The answer is a resounding "eh." The movie is not a must see. You can easily wait for this on dvd or streaming or whatever.
The cast is serviceable, for the most part. Macavoy, Fassbender, and Lawrence along with the rest of the huge cast do their jobs fairly well. The problem actually lies in the material they're given. There's just no meat to the script and the players suffer because of it. Fassbender (Magneto) does a very good job with what he's given. Lawrence (Mystique) is actually the centerpiece of most of the story, but again there's not much there. Characters like Angel and Psylocke are given maybe 1-2 lines during the proceedings.
I will not discuss much of the plot to stay away from spoilers. The problem with the plot is that character motivations are murky at best. Magneto makes some sense, but there's really only so many times you can do the revenge story before it feels stale. This is a man that saw his family and his people massacred by the millions by the Nazis. Did he really need MORE motivation or another revenge motif? That was rhetorical, the answer is no. Other characters have little to no discernible motivation, either to be heroes or villains. They're just there, and it's as lame as it sounds.
Very little. This movie is very talky. The action sequences have tons of CGI, which probably made Zack Snyder giggle gleefully, but it's not compelling. The entire world is in danger, but you don't feel it. It's just some cool rendering in photoshop. The "Wolverine" scene is actually pretty long and somewhat brutal, but it doesn't really mean anything. It's a cameo for the sake of a cameo, and has none of the charm of the Spider-Man cameo in Civil War.
Very little. It tries very hard to be very serious. There are some slight moments of levity, but they are few and far between.
I have always believed that great action franchises are defined by great villains. If that's the case, then this movie should not have been made. Apocalypse and his Horsemen are not particularly intimidating. Apocalypse's motives are not well defined and do nothing to elevate him above any other villain. The Horsemen have no motivations for being Horsemen. They're just bad guys because they are. It's all very by the numbers.
This movie is set in the 1980's, and had it come out then, it might have been considered a good comic book movie. But we've seen GREAT comic book movies (the Avengers, Winter Soldier, Civil War, Guardians of the Galaxy, Blade, the Dark Knight, X-Men, X-Men 2, and so on) and this is frustratingly meh. This franchise is in trouble. This was a reboot, for the most part, and it sucked. The new cast of X-men do nothing to make you want to see them again.
This movie is a D. No need to watch it in the theater. No need to watch it at all, actually.