On further reflection, I like it less than I did when I walked out. I went in looking forward to some 80s noir and future dystopian world, but left with the same kind of disappointment I had after I left The Last Jedi. If I had to point to two things, I would say the inept world building and the ending were my chief complaints (ignoring the book existing). The stacks are supposed to be an overcrowded pile of RVs where people live in desperation for energy and shank each other over government food stamps, but in the first five minutes we see a bunch of people getting drone delivered Doritos and Pizza Hut, plus the park looks a lot like a trailer park redneck passion project meets Willy Wonka. And the ending, Jesus Christ it made zero sense and was ripped straight out of Willy Wonka. And for the final touch, Spielberg tossed in a teaser that calls back to his work finishing AI at the end (wont spoil it, its super obvious) that had me thinking "Just dig up the dudes corpse and fuck it already, Steve." Really, the lack of significant Wizard of Oz style contrast between the Oasis and the real world is probably the biggest flaw in the movie.
On the topic of changing things from the book: Lip syncing Wargames would have been hilarious on screen, but instead we got another gay love letter to Kubrick in its place by subbing in the Shining. Dumping the D&D shit at the beginning also glossed over the entire background of the Halliday, Kira, and Og relationship and the fact that the first key was actually placed someplace poor kids could access it. And if we are trimming the fat, then why the fuck did they add TJ Miller and google eyes security chief diversity hire to the movie? Why the rewrite of the ending where three keys were needed with three people (symbolic callback to the Halliday, Kira, and Og trio) and we got a Street Fighter showdown in place of the hordes of people trying to beat the last game challenge simultaneously? How about the complete rewrite of the aunt into something sympathetic and no sign of Rush World?
I actually have a pretty good idea of what happened here, at least with some of the changes. Spielberg has good will with the Kubrick people, so getting access to his movie to publicly suck his dick on screen was probably easily done. The other things they kept were generally easy to get rights for (or he had them outright, like the Back to the Future shit). The CGI was deliberately retro (did not have to look realistic) and there were basically four physical sets all in the burbs of Toronto from the looks of it. Then there is the wall to wall product plugs in the movie. This movie was made as cheaply as they could, for whatever reason, which is probably why the only recognizable actors in it were Pegg and Generic New British White Villian guy. Somewhere along the line, this movie must have had some serious budget limitations placed on it or else there is zero excuse for the changes beyond Spielberg fucking it up to put his own mark on the material (or blow Kubrick's dead dick). That used to be an area where he made good changes (see Jaws and Schindler's List), but the dude has lost his touch and his edge. I think I am more disappointed in this movie than I was with Crystal Skull.
But....It IS a well polished turd. Pacing was really decent, as the movie did not feel as long as its run time suggests. Aside from the completely WTF Willie Wonka ending, the scenes blended together smoothly and there was not any absurdly out of place acting in the movie (except TJ Miller being himself). The final battle is a good spectacle. None of the characters are outright annoying or a cartoony caricatures. The special effects sequences play well into the story. I would compare this movie to Avatar; a movie a lot of people will praise but never watch again.