Multiple cart stowages with doors, where you have to open all the doors just to access one cart, are a PITA! Very annoying after a few hours... (Airbus mostly guilty of this I notice) Would be neat if the external doors would fold back into a recess, while leaving the cart latches able to be secured if needed (meaning not having to open the outside door every time you want to reach into a cart- otherwise, many aircraft this means if you leave the door open for ease of access the only way to secure the cart is the brake. Much prefer the doors which 'cover' the carts and latches, to the ones where the latches close the door (if that makes sense!) looks better too. And you know the latches are secure otherwise the door won't close in the first place.
Trash compactors are generally crap, though I think these come from separate companies.
Many of the fold down seats are too high to comfortably balance a meal tray on one's lap.
Sinks are generally down to the crew, and many galley 'issues' are really down to airline taking certain options and omitting others (like GWDU which is fab and should be mandatory on all ULR aircraft in my opinion!)
Th ability for chillers to switch off for a bit when they reach the required temps would be great (i.e. auto chilling) since often the galleys become iceboxes on long flights, and most times it's the only place for crew to go when outside of the cabin. If the chillers were able to self-regulate the temp to the preset/required level I am sure this would reduce the 'freezer effect' somewhat.