If you're looking for an affordable field recorder- this sucker is where its at. It records directly to .wav or mp3 so you can dump the files directly onto your computer and tinker with them. It features two great condenser mics for left and right stereo recordings and does very well just dropped in a room.
I've recorded many, many live shows with the H4, both for myself and for others and have very rarely been disappointed with the results. There are adjustable gain levels for the built in mics as well as a built in EQ function.
If you're an amateur home studio type then you're in luck- the H4 also has two combo XLR / 0.25 inch mic inputs for you to hook up your own mics. Run this via the enclosed USB chord to your computer with the cubase that comes bundled with it and you've got your own portable home studio (especially if you've got a laptop!).
One very important thing to note however, is that its difficult to surpass the 'extremely good field recording' and reach the actual 'studio quality' recordings because of one fatal flaw of the H4. Its marketed as a 'four track mixer' but in fact only has two inputs (each that can take EITHER an XLR cable or ¼ inch input, but not both at the same time). This makes close micing fairly impossible if not merely improbable. More so- each mic records only to the Left or the Right channel, respectively, so that what ever is going in one mic is going in the right headphone and whatever is going in second mic is going in the Left. If you know your way around some digital editing software (like cubase, or audacity) than this can be overcome by splitting stereo tracks into two independent mono tracks- but that still means that at most you've only got two tracks you can record to at any one time.
For the money however, there is no better tool than the H4 for field recording and amateur portable home studio use.