Some quick background: I bought my first 4-track recorder in 1989 or 1990, back when it went onto cassette tapes. That was a Tascam Portastudio, with pan and tone dials and sliders for mixing. Since then, I have recorded with an A/D converter into Cubase (early 90s), through a 32-track mixing board onto digital audio tape (mid 90s), and more recently, with a laptop and A/D converter in a few different DAW applications. I have also used several scoring applications, some of which supported audio file imports and VSTs. Finally, I have been a software developer for more than 20 years, doing mostly web applications and some mobile applications.
I bring all of this this up because I want to make clear that I'm at least experienced with recording and digital devices, so take this review with that in mind. In short, I find the Zoom H4N to be a great scratchpad, but I certainly would not want to use it for serious recording.
As far as recording goes, both the stereo option and what they call 4-channel (meaning two stereo microphones) are a snap to use. Hit one button to get input levels, hit that button again to start recording. There is a neat mark feature as well that lets you put a...er...mark when you want to note another take, another song, etc. These are useful down the road if you want to split the file into separate tracks from the marks.
Multitrack recording does not fare as well as the above options. The user interface has actually changed - now you don't hit the same button to record. You also have to set the recording mode purposely, either to record over what you just recorded or to punch in. Both of these together make the H4N feel a little wonky after using other methods (especially tape). It works, but I found myself expecting the H4N to work like it does in the other two recording options and was frustrated a couple of times.
The H4N can do a bunch of other things, including the above mentioned split tracks on marks, convert files to MP3, set up file type and bitrate, record automatically, store files in different folders, act as an A/D input to a computer, etc. Frankly, the device is really very cool and I've messed with many bits in it just to see them work. The issue is that everything is hidden behind many layers of menu. It just feels extremely clunky. There is no doubt that the H4N is capable, but you're going to have to work for it. The user interface could use some serious revamping. In a world of cell phones, going back to a clickable scroll wheel reminded me of my first cell phone from 1997, which was not a pleasant reminder.
Overall, I like this little device, because I can just hit one button and capture a thought (musically, I mean - it is a little heavy to use for audio note-taking). The recording quality even with the microphones on top is actually really good. I've been surprised as the ability to capture the tone of both a guitar and a harp. That said, there is no chance that I would consider using the H4N to do a real recording. Multitrack is not smooth enough. I have not tried using the H4N as an A/D input to a DAW. That might work well enough, although A/D converters are so inexpensive these days that I can't imagine spending the time to hook this up when I could get a dedicated A/D converter to stay hooked up all the time.
Final thoughts: The H4N is a decent device. If you're looking to do some nice recording out in the field, it works pretty well. However, Zoom makes a smaller recorder called the H1N, which can do much of what this device can do, with the exception of multitrack recording. But given how clunky multitrack works, I might recommend the H1N instead. If I wanted to exceed the capability of the H1N, I would probably move to a dedicated DAW.