The sequel always has to be bigger than the original, and more certainly is the approach "Deadpool 2" takes.
The "Merc with a Mouth" does more of just about everything: more talking, more shooting, more dying, more characters, more bad guys. The first "Deadpool" was self-aware to a meta degree, one where the main character continually broke the fourth wall to make snide comments and laugh at just about everything. Deadpool is the ultimate cynic, given the green light to make fun of just about everything at any moment, down to jokes about Marvel vs. DC, and the high-profile dual affiliations of one of this film's main characters (among many other things).
After a first film that mostly hinted at its affiliation to a larger world, the sequel goes to great pains to drive home where Deadpool resides and who his neighbors are. For those trying to keep score, he is not a part of the Marvel Cinematic Universe, but rather Fox's "X-Men" universe, which may or may not soon roll into the MCU...just go with it. For now, think Wolverine, not Iron Man.).
Also more plot, though the film is as ADHD-addled as its title hero, unable to focus for more than a few seconds at a time. Buzzing from one narrative thread to another seemingly at random, it takes awhile to figure out where the film is going. The main narrative involves a young mutant named Russell (Julian Dennison of "The Hunt for the Wilderpeople," a film you need to see NOW if you have not) who has broken free of the shackles of the "mutant group home" he is being held in.
Deadpool takes to Russell, and makes it his mission to save him, a job that gets even more difficult when Cable (Josh Brolin) shows up from the future, bent on ending the kid. But in between, we get bits involving some of the X-Men, a personal tragedy, and a couple of scenes where he takes out some bad guys. These scenes are interconnected, though it doesn't always feel that way.
In the comics Cable is the son of X-Men Cyclops and (a clone of) Jean Grey, a sort of human/cyborg badass from a dystopian, war-torn future: think if Kyle Reese and Arnold Schwarzenegger's Terminator had been fused into one being in time travel transit. He is straight-faced and mostly humorless, and has his own reasons for wanting Russell dead.
This puts the two at odds, and drives much of the film. The narrative importance of Cable isn't really defined; he kind of just shows up without explanation and jumps into the plot. This is fine, though, and with a costumed contract killer with a penchant for the tawdry and a knack for not dying no matter what happens to him, it doesn't exactly feel out of place.
Deadpool, recognizing he needs more characters with which to connect to a larger universe help battling Cable, assembles a team of third-tier X-Men, and dubs his group X-Force (an X-Men spinoff group with a long history in the comics).
But this is the kind of movie that loves to play with expectations, so without spoiling anything let's say only one of the group really does anything of substance, which is Domino (Zazie Beetz), whose mutant ability is perpetual good luck (along with some fighting skills, of course). She impresses, as does Brolin, who was also busy playing another Marvel character in a movie you might have heard of (and yes, the subject comes up). Dennison is terrific casting, a young man who doesn't look the part of a superhero, but has the chops to pull off a believable (future) villain while maintaining some empathy.
The movie tries to balance a warm heart while letting dick and poop jokes fly with virtually every line of dialog, and it doesn't always succeed in that. As jarring as it is to have lewd quips in the midst of what is supposed to be a serious, tender moment, director David Leitch (along with screenwriters Rhett Reese and Paul Wernick) let the serious moments be a cliche, and even tweak it from time to time.
And then there's Reynolds, employing the see-what-sticks method of quipping so much that he gets a writer credit as well. He bats better than .500, but there are plenty of groaners in there with the genuinely funny moments that you can overlook them or even drop a pity laugh or two.
Is this "Deadpool" superior to the first? I'll say sure, though I enjoyed both immensely. They are lighter in nature than the MCU and even the other side of Fox's Mutantverse, but the world-expanding is fun (and there are more than a couple of X-Men Easter Eggs to enjoy in this film), the jokes are mostly good-to-really-good, and the serious moments are...well, cursory, but there.