After playing an entirely different game prior to this, I had not that much time to play it. I only finished the first... uhm... "world". But I managed to find all secrets, which is what I am aiming for, since back in the days I didn't find every last one of them. But thanks to the internet I found them.
And before you ask: No, I haven't checked them before I played the levels. I checked them during the the playing of the levels :P
Yes, I know, it's somehow cheating. But I just checked the times where I knew I didn't found all.