I'm going to sound picky, none of these would stop me buying a house I liked but I'd want it changed ASAP. Most of these are from rented pads.
Conservatory
Old sash windows, they stick so you can't open them properly then the wont stay open on the latch and fall on your head if you lean out
Economy 7 heating & gas fires where you nearly break your thumb on the ignition can't believe people still have these
Concrete driveway and or patio
Decking, dangerously slippy, rotten, and hides rats and mice
Tiny box room bedroom number 3 waste of time and space if no baby
Carpet in the bathroom including anywhere with carpeted bath panels
Mezzanine floor bedroom
Completely paved/gravelled garden
Hot water tank in the bedroom
No window bathroom even with a decent fan
Open plan living room dining room kitchen, pathological need for privacy, I am British after all. Open plan kitchen dining room is fine, but need a room with a door on the lower floor
I would have added chimney breast but having discovered chimney sheep, the draft doesn't come through the chimney anymore
The one I couldn't buy is the one with a small garden, can't add to that so easily