Fair disclosure: I don't have the PHB so I'm working off of Basic.
1: I did not expect it to be as rules-light as it appears to be. It's very 'frame-work' like and not as much "here's a rule for EVERYTHING". coming off of 3e and 4e this has been the hardest thing so far to get used to.
2: Backgrounds. I freaking LOVE Backgrounds. WOTC could publish a 300 page tome of only backgrounds and I would be in for it.
3: CLERICS are interesting, fun and can do some neat things. I used to avoid clerics like black mold.