I was in Manila for 3 and 1/2 months back in 98. Personally I didn't like it one bit. The city is filthy. Trash is all over the streets and many times I couldn't even see 1/4 mile up the street due to all the smog.
When you start sweating, it runs down your arms in brown streaks the air is so poluted.
Then there are the pick pockets and thugs you have to worry about.
If you do go, make sure you never end up drunk out in public. ...and never except a drink from someone you don't know including other foriegners. They'll drug you, take everything you own and leave you naked in a ditch somewhere if you're lucky.
I've spent quite a bit of time in the P.I. and was wise enough to never get robbed, but I lost count of how many times I figured out I was being set up and got out of the situation.
If you do go, insist that where ever you stay has A/C. And if anyone ever comes up to and says, "Hey! I know you..." start walking the other way. You're getting ready to get taken!
Edited to add: My wife is trying to talk me into going back to Angeles City (where Clark AB use to be) to visit her brother and grand parents next summer. I'm doing everything I can to avoid it, but that's me. If you've never been before, then maybe you should consider it. It'll make you appriciate living here in the U.S.