It may be an exaggeration that Logan's reasoning for his depression is so paper-thin and nonsensical, but watch any number of prior X-Men movies and it becomes incredibly difficult to buy into. Which is a shame because the movie teases the mystery to Logan's failings often. Xavier, in the film Logan, comparatively strikes out of the blue with a startlingly horrific and believable revelation to the death of his students -- and this is lead up to with the actual cause happening (but prevented) in present.
At least Deadpool's character arc shows more warmth and humanity than his previous films. The mercenary's relevancy is at stake, both with a mid-life crisis and a commentary to the MCU lavishing it up. Whilst he really is nothing but quips, Deadpool values experiencing life with friends and family. The overall story, particularly Deadpool & Wolverine's utter abhor for one another, does a decent job reinforcing this.
But man. When I said Deadpool is "nothing but quips", that really applies to the entire CAST. All of them. Whilst I get that it's just the flavour of the franchise, and the Wolverine is no stranger to sarcasm, even the MCU leaned too hard on it. But hearing a bevvy of extended Marvel characters trying to drop spicy 15-rated jokes really began to annoy me. The raunchy jokes just evaporated by the half-way point and the laughter began ebbing from the audience around me.
Otherwise? The action scenes really are fast, frenetic and well directed. Cassandra Nova's unhinged familiarity is unnerving. It's tender to see so many past Marvel movies brought up to spotlight in the context of it all, as film fans absolutely have existed before Spider-Man and X-Men of the 2000's got the ball rolling.