One of the only reasons someone over 15 should enjoy legos(or other PBBs).
Its like playing D&D,Warhammer,or Warcraft; But with legos!
You can build the most creative/awsome deathtrap out there and send it screaming into leigons of yellow smiley warriors.
Very fun indeed.
If your any type of wargamer(RTS too) or not, you should check out www.brikwars.com and then bring out your old legos and let the destruction ensue!