I did not buy the physical version of the 5e Monster Manual 2024, I bought the digital version for Foundry VTT, so some of the things mentioned I have not experienced.
Overall: Simplifying the monsters overall, but specifically the abilities and writing them down more efficiently is imho the biggest advantage of the new MM. I can now quickly glance at monster and run it right out of the box. Making monsters simpler to run is a huge, huge bonus in my book!
The 'removal' of Lair actions I approve of (disregarding the mostly harmless effects), I found it extremely quirky and the added strength didn't add anything to the CR or the reward, which I found odd. I would expect that this would lead to a lot of D&D sessions being reduced to luring monsters from their lairs and slay them outside before claiming the treasures inside...
The art... I dislike quite a bit of it, and especially dislike the shared scenes in the MM. I do like scenes in general, but I don't if that's the only depiction of the creature in question. In some cases it's difficult to determine quickly what is what and showing players shows them everything in that creature 'family'.
The removal of drow, duergar and orcs in the MM I find particularly egregious, and the replacement stats are really bad, especially for the drow. Some claimed this was due that these creatures were no longer to be viewed as monsters, due to 'racist' perceptions. Imho that kind of reasoning made me facepalm, but OK, I can accept that to a certain degree for other people's sake. But then WotC came out with Adventures in Faerun: You want Drow stats? Here, pay $75 for this book! At this point I'm curious which $75 books in the future will feature the Duergar and Orcs (of course one per $75 book)... Sidenote: drow, duergar and orcs are in almost all settings, FR, Greyhawk, Dragonlance, Eberron, Spelljammer, Planescape, Mystera, etc.
What I find annoying in this 5e 2014/2024 is the lack of simple treasure. You're telling me goblins or bandits don't have a few copper pieces on them? Also the changes to things from Humanoid to Fey for example really mess with some adventures, i mostly just ignore such restrictions.