This scope has been out long enough that most people who had to have one right away already bought it, and enough folks who bought it put up reviews, so I won't wax eloquent about it, but just summarize my own findings in case they come in useful.
I bought this scope almost two years ago and I have used it extensively in my work and travels all across the arctic, and at home it stays right by the window (I am lucky enough to have a house perched atop a steep cliff overlooking the ocean) where it is on standby just in case something good flies by (which happily is fairly often!)
I chose a straight scope which I find are vastly superior to angled designs for ease of locating birds, and most importantly because of the minimal fatigue associated with looking through them for long periods of time. If I try scanning for bands for two hours with an angled scope, I can barely stand up straight afterwards!
The scope is very nicely constructed. It is pleasantly heavy, and the housing is done in a very nice slightly rough finish.
The front lens is recessed well into the body for good protection, and a sunshade (plastic) slides out very smoothly and easily to offer protection from flare and glare as well as dust and water. This is well designed, and there is no play at all, the shade is perfectly fitted to the main scope tube.
The tripod mounting ring is also very nice, and allows the scope to be turned to any angle once mounted. I like to tilt it a bit to the right to allow for easier and more comfortable focussing.
The eyepiece I got (20-60 zoom) is equally pleasing. It comes in a handy little bag with nice rubber covers to use if you take it off the scope. It attaches with a bayonet mount mechanism (like camera lenses) and it slides smoothly and very firmly into place, snapping into position with a very satisfying click. To remove it, you depress a small button near the mount and twist it back out. The eyepiece has a very nice and large knurled zoom ring that is easy to turn and has a very smooth action. Magnifications are engraved along the barrel. The eye-cup is nice soft rubber and clicks through two stops and offers excellent eye-relief. The lens itself is quite large and allows for more than a bit of leeway in lining up your eye to it. You can look slightly askance and still get a nice full image.
The scope uses a very nice double focussing mechanism, a larger knob that is for quick co.... focus (which I rarely find myself using, perhaps only when shifting from a distant bird to a very very close one) and a smaller fine focus that is right next to the first. The feel is smooth and firm, with a very fine 'response'. It takes very little movement to shift the focus.
The image quality is nothing short of superb. Complete edge-to-edge sharpness with no flaring or softening, even at full zoom.
Colour cast is perfectly neutral, and no tinge is apparent at all.
The field of view is excellent, although I have heard the 30x fixed eyepiece is even more impressive. I would however suggest (without the benefit of comparison) that the real advantage in this scope is the ability to fully use a 20-60 zoom. Even at 60x the image is perfect. Sharp, vibrant, breathtaking.
The depth of field is a bit of an issue, but it seems to be at least as good as most other high-end scopes out there. Certainly at full zoom and close range, it is hard to bring an entire bird into focus, and even at 20x reading bands on a flock 30 m away involves quite a bit of adjustment. Having said that, this distance is pushing it to a bit of an extreme, because you would be well within binocular range.
Pulling in a distant speck on the horizon or trying to pick out a blur in the haze half a mile away across a mudflat is where this scope shines though. Even in low light, zooming in is a delight. Very minimal loss of light (thanks to an 88mm objective) means that image quality remains superlative. The one drawback (one which has nothing to do with the scope and everything to do with a tripod) is that shakiness can become a bit of a factor.
The only times I found myself getting frustrated was trying to bring a distant bird into clear focus through heat haze or rain or fog or whatnot, only to inevitably realize that I could not possibly hope to ever do better. Using this scope alongside a few older Kowas (including the still-excellent TSN 4) proved this point time and again. This scope is so good, it constantly tempts you to try and do the impossible and identify birds absolutely beyond the limit of conjecture!
I would highly recommend investing in a top-quality tripod to go along with this scope, and I can also recommend (in general for any scope) a ball head. I find there is absolutely no better system than a good ball head for maximum comfort, versatility and ease of use. Panning on non-horizontal angles is a piece of cake. One handed operation is the norm, and also a very nice bonus is the ability to fine-tune the scope position relative to your eye when sitting in a blind or an otherwise cramped and uncomfortable position. WAY easier and more pleasant (and effective) than constantly trying to move the tripod legs up and down and in and out never quite getting it right.
Cost, if it must be considered, and let's be realistic, this is not a cheap scope, is I feel fully justified. This scope is an absolute gem, and will no doubt last a lifetime.
As a final note, I would caution potential buyers that Kowa has not overly impressed me with their customer service, namely a very long turnaround time for service.
Shortly after I bought the scope, a small piece of dust within the eyepiece was knocked loose and settled permanently on the lens. Even though it was only visible at 20-30x magnification, it drove me insane; it looked exactly like distant flying bird when panning. I sent the scope back, it was serviced (for free, including shipping), but a few months later, the exact same thing happened again, right down to the position of the speck! I finally asked the fellow I bought it from to help me out and trade me eyepieces so he could deal with Kowa and the 3-4 week turnaround, which he was most gracious in doing.
Kowa did send me a free lens cover to replace one I lost though, and they were pretty nice on the phone. I am just a bit put out by the long turnaround and the apparent lack of good quality control. Having said this, I feel that I must have just been unlucky, since everything else about the scope clearly indicates a tremendous attention to detail and quality.