Hello there!
I recently built this diner.
I have recently began to start work on more “Detailed Builds” and thought it would be cool to make a small diner.
And yes the windows are transparent, its just night outside.
Pictures:
Heavy criticism is appreciated.
It could use more detail. The walls look plain and empty. Most diners have pictures and signs on the walls.
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.
Here’s some pics.
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.
I think you could use a bit more decor like pictures on the walls and some more lighting would be good.
I must have forgot to mention this, the diner is supposed to be “creepy” and have used it for a myth build showcase.
It looks good if it’s supposed to be creepy. But, I would add some more details on the walls. Like some darker parts to make it realistic. But so far it looks good. 
It’s kinda plain, maybe add some decorations and stuff to make look not as plain.
If I were I would also maybe scale that into the wall, as you scaled outside which kinda looks weird.
Suggestions for improvement:
Give the walls much more detail to make it more appealing. Add some paintings, frames, curves of the wall structure, and different colours.
Change the windows, I am not 100% sure if those are curtains or not. But, I would actually add detail into the windows, add parts on the bottom and top and adjust to your likings.
Add small details, these matter! You could add a register, books on the shelfs, food items on the shelfs, glasses on the shelf, plate settings on the tables, table covers, etc.
Change the lighting, it looks way to dark. Make it a little bit lighter and perhaps add a small amount of yellow, red or orange to give it that nice welcoming look.
Change the chairs at the bar, make a small ending on the bottom. They look like they’re currently connected to the ground in a way, they should have some type of bottom to it.
Hello!
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.
Here’s a reference image-
Good luck and thank you for reading~
