Actually I've been playing each episode in one go, so that can't be perfect. It doesn't have to be either, does it? :-)
I intended to visit all secret areas. I think I missed one in episode 1 because I did it all from memory, but then I did some research and planning for episode 2 and I think I got them all. I'll have to recheck, though.
I killed most monsters, but sometimes I skipped some to keep up the pace (shooting repeatedly at 3 cacodemons trapped in a room through a window is not what I call entertaining).
And don't count on me to collect every single health vial and armor piece. Too much work, not fun enough.
Don't know if I'll be going for 100% secrets in the fourth episode, because I'm not familiar enough with it. We'll see.
All in all, I try to be thorough without becoming tedious ;-)
On the other hand, you'll find a 100% speedrun on
Speed Demo Archive but that one was so blinding fast that it made my head hurt and almost made me throw up! :-D