SyZtheActuary: First I play through the 4 campaigns on Ultimate Doom, then I play everything in Doom II + Master levels (how many levels is this ... ?), and then I play Final Doom (how many levels is this ...?)
And THEN I start playing .wads that other people have made and I can basically play forever?
Basically.
Here: just for the documented levels (those that have an article for them created): [url=http://doomwiki.org/wiki/Category:Levels_by_name]1485 pages[/url].
As for the id-published levels:
Ultimate Doom: 36 (32 normal + 4 secret)
Doom II: 32 (30 + 2)
Master Levels: 21 (20 + 1)
Final Doom 64 (2 x (30 + 2))
So in total: 153 levels, including 11 secret level.
SyZtheActuary: Also, I don't think I've gotten anywhere near par, like ever. 2 minutes on the second mission and it took me 23 minutes and I missed 80% secrets? lol
Basically the par time is for people who have played through the levels several time and want to see how fast they can blaze through it. It's generally impossible, even with perfect knowledge of the map, to get 100% kills/items/secrets and be under par: beating the par time is only for when you take the fastest route possible and ignore any distraction.