What aspects of your product must be flawless before its release?

I've struggled with this very question myself. I would agree with other answers that your product should for the most part be bug-free (although a few unnoticeable issues also won't hurt if your end users don't see them). However, in addition to that make sure that the core aspect of your product works well enough to provide value to your end users. It doesn't have to include all the core features in your long roadmap, but make sure that it there is enough for someone to use it and see enough value to come back a few more times, otherwise you won't really get the usage required to get valuable feedback from your users, which is the most important thing for long term success.