I think Uatu hit it on the head - it's like a computer game on paper.

When the computer is handling all of the complicated stuff , it's not too bad. But when I downloaded the SRD (the Open Source rules set) I realized that it consists of far more rules than the 1e PHB, DMG, UA and 2e PHB and DMG combined. Really? you ask.

Yes, if you don't count the examples and graphics in the in those 5 books.

There's a lot of stuff.
On the other hand, I'm sure that just like with 1e and 2e, you don't need to know every single rule, or even use them.