The diversity of the new legos is amazing (as said in other comments). We were happy with very basic stuff (like castles, spaceships, etc...) made of a few species of blocks. Now... Much more shapes, colours, etc...
I actually recovered a few months ago huge boxes of legos (that was dying somewhere at my parents') that I was playing with as a kid, and my 5 years old son is now the happiest kid on Earth ^^