The gunslinger is definitely a hard one to get going (but it does get going) because he was super young when he wrote it (I think he was like 19 or something like that) but overall the Dark Tower series is one of the best pieces of fiction I’ve ever read. Especially if you’re familiar with his world building (lots of books live within the Dark Tower universe like The Stand, Salem’s Lot, even The Shining to an extent). It also has one of the most memorable open lines of any book series “The man in black fled across the desert, and the gun slinger followed”.
Check out some of his novellas like The Langoliers, If It Bleeds, Elevation, etc. They are shorter reads (for King at least, usually only a couple hundred pages) and generally get straight to the point (instead of spending a chapter describing a scene).
That and his short stories are some of his best work. It might make you want to jump into some of his more iconic stuff or allow you to realize you don’t love his writing style and save you a couple thousand pages.
The Boogeyman is my favorite short story from him. Jerusalem’s Lot is also the short story that Salem’s Lot comes from. Another great read.