I think the biggest problems here are twofold and connected. Leaving the "Official but not following Maxis Standards" new builds aside, because they are not as bad as pure gallery builds, it's the combination of Clutter and MOO. And with Clutter I mean all clutter, not just what is categorized as "Clutter" by the game. An abundance of plants placed with MOO is Clutter in this regard for example.
First of all pathfinding and actual physically impossible to use objects of course, most often thanks to MOO and no testing.
Second adding 10 000 pieces of clutter making not only the lot difficult to use on low end computers, but also very often it's the clutter that pushes the "Starter home" (according to the builder) into a price range where you literally have to cheat to use it as a starter home.
(People calling things starter homes that isn't is a related can of worms just like people just assuming you always have MOO enabled).
Third, with the platforms now introduced, is the "Platforms EVERYWHERE" problem. And this is a problem I also see with say James' lounge in Snowy Escape; the stage looks great, but since it is treated as a separate room by the game, if you Perform on the piano, the townies walk up on the stage to listen, they don't sit on the couches since they are in a "different room" so unless they have no choice, they will walk up on stage (and I realize he couldn't know about this beforehand).
Fourth: The Medical Examiner's lighting phenomenon, where builders somehow desperately need everything to be brighter than the sun. I have literally removed two thirds of the lights from the Mansion I now have remodeled just to get beautiful and realistic lighting in it.
Fifth: Houses that are so dependent on MOO that if you place them unfurnished and try to furnish them without MOO, it is literally impossible to get full functionality since you cannot get a functioning kitchen in without MOO for example with whatever room dimensions and door placements chosen by the builder.
I think these are my most persistent pet peeves at the moment.
