Only does it matter if the guy has a really, really big penis, so that it is uncomfortable, or if it is really small, so you cannot even feel it. Everything in between is okay. My husband is about average, and it works for me. Really, the foreplay and stuff while you are having sex makes it better. Different things are exciting for different women.
I cannot usually get off just from having sex, anyway. He will have to go downtown or use some sort of toy, or else I will. All actual sex does is get me turned on. For hub, there are many ways of relief. Sex, oral sex, or he or I playing with it. I do not particularly like my husband to get off first. He loses interest.

I do not think I have one of those G spots.

My favorite is if we have plenty of time to mess around with no danger of kids running in. I like for him to mess around and have his mouth and hands all over me. If I can get close, and then back off, and repeat that a few times, when you can bear no more and go for it, trust me, your pleasure will be much more intense and long-lasting, I kid you not, I damn near saw stars, and put claw marks all over. I was one horny beast!

But for the vast majority, the variation in size is not that much, and unless it is extraordinarily big or small,its going to be fun. And don't trust it if a guy looks like he doesn't have much when he doesn't have a hard on. Sometimes, it gets a lot bigger! Lol