A Russian joke says that a really good sex is when even the neighbors light a cigarette afterwards. Now on a more serious note…
I can get good sex easily. Good sex is something that feels nice and makes me come. I can get that under most circumstances with almost any partner in under a minute, and it’s even easier than orgasming from masturbation. But it doesn’t leave a lasting impression. For me, amazing sex is something that surpasses certain limits:
It surpasses my expectations (“I had no idea this could feel so good!” or “I knew it could feel great, but this is even better than I thought!”, or even “Wow, I didn’t know it worked like that!”).
It clashes my capability for enjoyment with my desire for it (also known as “I can’t take it anymore, do it again” or “No-no-nye-yes-yes”).
It overstrains my body (common symptoms: pain in muscles the next day, coarse voice from too much screaming, bruises, hickeys, marks, maybe broken nails). I may start fighting or trying to escape.
It overloads my sensory capabilities (I can stop hearing, perceiving time, registering what is going on around me, my feeling of pain and discomfort numbs down noticeably). I may start talking gibberish, mostly on the dirty side.
It makes my mind transcend into some other plane (I switch off into nirvana, float in space).
My personal symptoms also include: crying from strong orgasms, inability to move or walk for a few minutes afterwards, vertigo, minor headache, maybe passing out (ah, vasovagal response, that little darling), buzzing and numbness in my head, major hunger.
And it makes me want more even as I lie there knowing very well that my body and mind have been totally squeezed out and “more” will be just plain dangerous. So then I refer to this kind of sex as “What the fuck just happened?!” and my partners sometimes joke that “Felt like a sex bomb went off here.”
Which is to summarize: if you’re not going, “wow, this was outstanding!”, my guess is, it’s not. You know amazing when you see it.
… Oh, and about those neighbors - if they knock on the walls, that’s a sure sign that sex is amazing.