Just a personal experience, yours may be different with mine.
The most FAQ: How good the sound quality is for the Zen Micro?
If I compare the sound quality with EMU series and ESI Juli@ soundcard, that will be unfair. But even comparing with SoundBlaster Audigy series and M-Audio Revo series soundcard, I still feel that the output of soundcard still sounds better. Maybe that's me, but I do wish to have a dedicated DAC for audio output instead of using codec in MP3 player.
Anyway, if compare with other competitors such as iPod, especially 3G iPod, which I have listened quite a number of times, it is no doubt that Zen Micro sound better, at least on my ears it do sound better. No idea comparing with iPod Mini, since I don't own one. But my friend who listened to both prefer Zen Micro.
Never had a chance to play with iRiver players, thus cannot comment much. The same apply to RIO Karma/Carbon.
One thing for sure, during my listening session using Audio Technica ATH-EM7 headphone, I found something is missing: Details. I compare the ATH-EM7 headphone with Bang & Olufsen A8 earphone (thanx to Gerald), as well as Sennheiser HD202 (thanx to Clement). The comparison result makes my doubt become more realistic. In the comparison, HD202 has the least details, because it render almost everything to low frequency. But comparing ATH-EM7 with B&O A8, ATH-EM7 definately is losing the edge.
That translate a better headphone when pairing with Zen Micro, it do sound better. How much budget to strip for a better headphone is much depending personal preference.
Oh, it do really look "cool" when it was at night. I remember it was night time when I travel last Thrusday. The glow do looks interesting in the dark and that really attract many people attention.
User interface is simple and straight forward. So far ok for me though I do not read any manual. Until when I want to manual scan a FM station then only I ask for my friend's help, and that's the only help I asked so far.
Do I have any gripe with Zen Micro? Unfortunately yes.
My main gripe is most of my Chinese songs unable to transfer using Zen Media Explorer. All the Chinese songs play well in my Win XP system at home, display the Chinese characters accordingly, thus I do not understand why Media Explorer cannot see the song title as in Window Explorer, and of coz cannot transfer the songs too. All it can see is only ??.mp3. Yes, question marks, that's what it seen. My MuVo does not have this problem.
So I try out this morning again at home, instead of using Media Explorer, I use Window Explorer to drag and drop the music files to my Zen Micro. Woolah!!! The Chinese songs transfer without a problem. But when I turn on my player and try to playback the files, I cannot find my Chinese Songs in my units. I have no choice but plug it back to my system. Accessing the unit by using Window Explorer, the files are there. Open up using Media Explorer, yup, the files are there. After a few thought, I decide using Media Explorer to create a playlist. Unplug the unit again from the system, search for the playlist that I created and play. Yup, now all the files are there. Though the songs still show ?? or ???, but now they do play fine. I try again by playing "All Track" under Music Library, all the files are there and can be play too. Guess I must mess up something previously.
One more thing: FM Receiving is not that good. I am ok with it, since I seldom using any MP3 players for FM listening nowadays, but I can feel the frustration of users who use it to listen to radio equally to mp3 songs.
About the touch pad, I purposely buying the black color player to try out this. Every button works fine for me except the BACK button. I need to tap slightly above the back arrow silkscreen instead onto it, and I need to press it with my whole thumb and sometime I need to press it hard, so that it is activated normally.
I have not used any other Zen Micro functions/features, I do not think I will as of now. May be others will use. If it have games such as Brick, that will be good and most likely I will use it, though may not frequently. After all, it is just a MP3 player for me.
I will be appreciated if there is separate charger to charge up the battery, so that I can still use my Zen Micro freely rather than stuck in one place if I have extra battery.
That's all my personal experience with Zen Micro, any input is welcome.
[Edited] more variant soundcard option.