In the kitchen is one of the ovens really low down? That would put me off, it's almost on the floor. Because the rest of the room doesn't really have any features it's one of the first things I noticed. Can you add some colour (apart from the stools!) with some flowers, pictures or a fruit bowl? I'd take down the family photos too.
Picture 5 really puts me off, where is the front door? There's a blank space on the wall where it should be and you've only got a side door? The huge expanse of blank wall on the other side of the single window downstairs looks awful. It'd stop me viewing the house as it doesn't seem to have enough windows. The window in picture 4 could be a lovely large window right across the room letting in lots of light but that'd cost ££ to do. Picture 6 - have it retaken without your car blocking the window.
Picture 7 - move those storage boxes for the photo and turn the eye cushions over!
Picture 8 - add some splashes of colour. Is there a window? Have the picture taken showing it, I wouldn't want a bathroom with no window. That would stop me buying a house.
Picture 9 - add some interest with a picture or flowers. Make the bed look really good, there isn't much else in the room to look at to make the room appealing.
picture 13 - what is wrong with the wall to the left of the window. Tidy the curtains - use a tie back.
picture 14 - the extension (?) takes up too much of the garden. That would put me off, also it's got a flat roof. I would not entertain the flat roof; we spent a lot of money to get rid of the flat roof on our house and it was a fraction of the size of yours, I got sick of sweeping water off it when the ice melted in the winter. We don't live in the frozen north either but when it rains it'd freeze in winter and then melt and not all drain off.
Picture 15 - the extension needs more windows.