i went to the Diner on Clifton about two years ago and remember it being good, but my experience today shot that "good" through the roof.
I have the yellowfin tuna sandwich and my friend got the Manhattan Rueben. Both were by far two of the best sandwiches I have ever tasted. The fish was perfect, the caper mayo was phenomenal, the slaw on the reuben was delicious (I don't like slaw) and the sweet potato fries were perfectly crunchy on the outside and steamy on the inside.
The atmosphere is exactly how a diner should be. You can see the kitchen and it's really fun watching what goes on back there. The bar is also a cute addition and I'll probably sit there next time. I didn't go to the restroom, but I did notice that you have to walk through the kitchen a bit to get there, so that's a tiny bit weird...but certainly not off-putting enough to turn me away.
I'm not hungry again yet, but I think I might go pick at my leftovers soon...