I have now played a game with *SOME* of 11th edition's rules, and have been reading up on the updates.
I know it's controversial, but overall, I really liked 10th edition. I've been playing since about halfway through 8th, and 10th was the first edition where I didn't spend an entire hour every single one of my turns to eventually go "I HAVE A STRATAGEM FOR THIS!" The detachment system worked far better for me. (though one of my spiciest hot takes is that 40k doesn't *need* detachments/subfactions, there's plenty of variety already)
While I am mostly a narrative player and am obsessed my My Guys #myguys, I didn't mind the lack of customization options. At the end of the day, Larissa Morrow, third Captain of the Iron Ravens and Military attaché to Lord-Captain Camina Baltazar is a Space Marine Captain. A commisar's a commisar.
I didn't really notice the lack of psychic, but I also don't play psychic heavy armies. (I guess I play Tyranids but I only ever played tyranids in 10th) though I totally understand why people were pissed.
And those end-of-edition supplements? We were eating GOOD. Crucible of Champions is wonderful and I'm having oodles of fun mapmaking and reworking the 500 worlds campaign system for 11th. Waiter! Waiter! More of this!
My biggest gripe with 10th edition was terrain. I feel like things were still pretty healthy at the start of the edition. I remember playing on boards with bridges and volcanoes. But as more and more tournaments were played, the options slowly vanished. Now, pretty much all my LGS has is WTC ruins and undecorated plywood area markers. The effort to make a perfectly balanced competitive meta made the game substatially less fun for everybody who isn't a hardcore minmaxxer.
Looking at the big changes in 11th, I see a lot of things that I think *could* work, but are being implemented TERRIBLY.
Like the new detachment system. I like being able to pick and choose multiple buffs based on my army, and not have to build my army around a particular buff. I can play the things I WANT to play and make them good. I even like... the idea... of having my army list determine what kind of game I play. Bringing lots of fast sneaky things gives me missions more about taking points and doing actions than killing stuff? Love the concept. But the force dispositions are not balanced. If your mission is "do actions (meaning not defending ypurself) on objectives" and your opponent's is "kill anything standing on an objective" my opponent might as well take the W because I can't win that.
With the detachments themselves, I feel it would work... if you start fresh with every codex. Having 2 editions worth of detachments in 1 edition is going to be bloated and exhausting.
Bringing back weapon option points ONLY FOR CERTAIN MODELS is just silly. Either commit or don't.
And Then There's Terrain. And again, I like what they're going for. Terrain features having a perimeter that determines In Cover vs Not In Cover works (mostly).
I also like fighting over terrain features more than I liked fighting over poker chips. That bit 100% succeds in achieving the greater narrative focus they were going for.
But, now that terrain determines where objectives are, You Have To Play With The Standard Layouts. I straight-up can't use the mission deck without that restriction. It's now WTC or nothing. I can't use the hive world board I spent a year and a half building because I can't place a ruin in its exact center.
And again, you could have implemented this fine. Every mission has six objectives. at the start of the game, each player nominates one terrain feature in their deployment zone and two in no man's land to be Objectives. But no.
Fortunately, when doing narrative play, you can fudge the rules. There are good ideas here that I can wrestle into something workable for my 500 worlds campaign and possibly my LGS weekend campaigns, but I shouldn't have to rewrite half the rules just to make this game fun.