The game has 32 (or 34 depending on how you count) regular levels, with a complete story ark told over that series of levels.
After that, there's mostly just speed running challenges. BUT in order to provide some reward for the speed runners, there are 5 additional levels and a followup story line / grand conclusion that can only be unlocked by speed running. I call this the Epilogue. It is now finished and part of the game. Lucky, since the game releases tomorrow (Dec 4th).
If you aren't into speed running but feel like you are missing out to not get to the epilogue, I feel you. But our speed running challenges are fairly mild, and more about finding the most optimal path, not split-second timing. So you might enjoy them despite yourself. And there's rumors of a way to bypass some of the speed running challenges, even...
PS if you are into speed running in a hard-core kind of way, you can always compete on the world leaderboard for each level. Being the best in the world won't unlock any extra content, but it might be fun, and isn't that the best kind of content?