I did love re-visiting Berlin, a few of nice things about it:
- lots of people on bicycles, thus less cars traffic 
- fantastic public transportation
- lots of nice cafes, restaurants, places to hang out
- Tiergarten, their central park, amazing
- many historical buildings and museums, have been completely re-built, refurbished
- you either feel a scent of linden...or marijuana :)
- fantastic beer places, in the nature, or just fantastic beer places
- all kinds of people. but good, peaceful vibe