Flatiron Mesa is one of my favorite hikes in the Phoenix area. Like other reviewers have stated, once you've gotten used to Squaw and Camelback, give this one a try.  It'll kick your ass.  It's about a 2600' climb in elevation, so you're doing more like 2.5 Camelbacks. You'll be scrambling over boulders most of the way up since there really aren't switchbacks. I'd say give yourself about 5 hours to go up and down.  It's inside Lost Dutchman State Park so you will need to pay an entry fee.

My one recommendation besides the obvious ones (being fit, pack food and water) is to bring some light gloves.  Since you're climbing up and down on all those boulders your hands will probably get a little scratched up.

Don't feed the wildlife.