I grew up as an avid and intense Lego fan, but eventually gained the mindset that it was a "kid toy" and so I passed all my sets on to my younger brother, and moved on with my life for a time. Then, near the end of my college education, I started to really miss my Legos, further motivated by a brother in law who also really loved them, and so I decided to get back into them. I asked my younger brother if I could have my old Legos back, and found that he too thought they were "kids toys" and hadn't touched them in years (but he still managed to ruin my organization system and lose some of my favorite pieces :P).
I have an equal love for building sets made by Lego designers and creating my own designs. I really enjoy seeing different people's ways of making things with a building block that is simple and easy to understand (and doesn't require an engineering degree). However, I have to admit that my favorite MOCs are those that make me forget they're made of Legos, or similarly, those that I am surprised are even possible with legos.