I have two Micros, gave one to my mom. She plays Warioware.
I've never had a problem with the size. My hands are fairly average sized and I love playing my GBA games on it rather than on my DS. The smaller screen is no problem to the eyes if you've got an ok vision, and my shoulder buttons haven't died on me yet (my DS L button did though).
The only troubling task with the Micro is the start and select button placements. They're on the edge right below the screen, so you have to shift your fingers to press one of them.
But, I love playing RPGs and shooters on the thing. With the size, it's as small or smaller than any cellphone, so it doesn't stretch your jeans out and make you walk weird when it's in your pocket. It comes with a little pouch thing to keep it safe-ish, along with a microfiber cleaning cloth. Depending on what type of Micro you get, it comes with replacement faceplates, so when you really, REALLY fuck up your faceplate screen, you can just switch the faceplate out with something else. It's a damn shame Nintendo never came out with those faceplates they said they would have.
I'm playing Fire Emblem on mine right now, its working out great. I've had no hard time trying to read what it says on the screen, and the buttons feel nice and clicky. I also used mine to beat Metroid Fusion at 100% in 2 hours and 2 minutes (FUCK). It felt like I had better coordination than when I played Fusion on my DS.
But that's just me.