Pros: Amazing sound quality, great range of file support, gorgeous look, clever interface, regular firmware updates, no software (e.g. iTunes) required
Cons: Small harddrive space
After my Creative Vision: M (60gb) broke in the Fall of 2010, I was considering getting an iPod to replace it. Thankfully, my brother directed me to this.
Upon receiving the item, I was immediately overcome by how gorgeous the J3 is. It has a small, slender, sleek black build; it feels comfortable holding it in my hand. Then, when one turns on the device, we're greeted with a rather quirky interface. From the bubbly sound when you press a button on the screen (which can be turned on and off), to the various icons which take some tinkering with to fully comprehend, the Cowon interface is admittedly quite strange compared to both Creative and Apple products (but incredibly flexible once you understand how it works). There are 3 menu styles, the default square grid, a grid list, and a sort of 'desktop' in which you can drag around all of the icons and arrange them in any way you like. It would be too long-winded to go into detail about the menus and all three interface styles, but suffice to say, they take some playing around with to get a feel for. If you made it this far on the internet, the learning curve should be no problem.
As for the rest of the pros, they speak for themselves. The J3 can play all the file types as described - whatever I threw at it, it played with great clarity. The sound is fantastic, even more so with high-grade equipment. The equalizer and sound settings can give you many different feels in order to get the sound you desire, and the volume on it can go quite a ways. At a volume of 20 (the maximum is 40), it already quite loud, more so than at the half volume setting for an iPod or Creative. In fact, using Shure SE530 earphones, listening to music at this volume for more than 30 minutes started hurting my ears. I also tried the J3 with my Sennheiser HD595s at the same volume with excellent results (no amplification, will update this review when I get a suitable amp); the sound is quite neutral, with crisp mids/highs, exactly how I like it. The battery life at a sustained volume of 20 can easily last you an entire day, though I haven't done extensive testing with the battery life to say much more (e.g. how long it can play movies before dying out).
In addition, browsing through the files on the J3 is similar to browsing through the files on your computer's hard drive; one can simply copy and paste files from a computer straight to the J3 with no software requirements, make new folders and rearrange them as you see fit, etc. This makes it very easy to work with. The regular firmware updates are just icing on the cake; many, if not most of the bugs that the J3 had on release have been remedied as of the writing of this review (including the dreaded playlist bug).
Admittedly, if you've amassed a great music/video/picture collection, with most of your collection in a high grade file format, 32 gigabytes of hard disk space may not cut it. This is rather unfortunate since one of the main appeals of the J3 is its ability to play high-quality audio files such as flac; a trait that can't be fully flaunted with such measly disk space. Even at the time of its release, the J3's competitors were easily boasting +60gb hard disks. If not for the first two pros I listed, this would be an inexcusable shortcoming.
As a final note, the J3 can't connect to the internet and isn't a phone. I mention this because these are two popular features to have with todays culture. Fortunately for me, I care for neither of them.