Looks pretty nice. Like @bulgee said, the walls could use some pictures. Also the tables could have salt and pepper, cutlery and sauces. Just something to fill up the space! Otherwise, nice job!!
Also, personally I would make the shelves behind the bar desk there, wood, not wood planks. Just looks odd to me.
I think you’re on the right track. The flooring, booths, and counter/stools are on theme. I question the shelving behind counter. Bars usually have a wall of shelves. Diners have a shelf, a window/door to the kitchen, and a messy counter for prep. Going from memory, most traditional diners are rectangular, longer, and don’t usually have a center row of tables/chairs. Usually older diners have a row of booths and a counter. I’ve only seen tables elsewhere, like outside or in another section. Denny’s, Shoney’s, Village Inn and more modern diner restaurants are different, but if you are doing modern diner, I’d change the flooring and colors.
The lighting is pretty poor which you can see from the dark corner in the last image. Many of the chairs have paper-thin seats and backs which looks like if anyone sat on them they would snap. The tables in the dining booths have no supports which makes it look like they are floating in mid-air. Not a fan of the blinding neon stripes on the counter either, try lowering the transparency or making them thinner so the glow effect isn’t so profound.
This is looking pretty good so far! I really like the well-established theme of the diner. If you’re going for a “creepy” look, I suggest adding lights. (A handful function while the rest are burnt out.) I also recommend adding plants that are intentionally overgrown or rusted metal to add to the “creepy” atmosphere. You could also add condiments, plates, glasses/mugs/cups and posters so the build isn’t as empty.