This lens is a great buy. I'm not professional photographer and this is the first lens I have bought for a digital camera (Panasonic GM1). I had a canon AE1 with a standard 50 on it years ago and liked shooting with it. The kit lens on the GM1 is good and small and great as an all-around lens, but as soon as I attached this one, my pictures started to improve. The proof is in the pudding as they say.

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size/weight
good and consistent IQ; but see weaknesses
versatile and useful focal length as a prime

chromatic aberration performance
screw-on lens cap is not practical

In short: decent lens, decent price, fun to use, not for everyone.

Let me get my technical observations out of the way first. It's very small and light, and very easy to wield. I'd avoid this lens if you only had an E-3, but on any other model is a welcome change from using a big zoom. It comes with a screw-on lens cap. It's very thin and looks nice, but kind of a pain to deal with unless you leave it off most of the time. I replaced it with a generic center-pinch cap and while it extends it's storage size a bit, it's more convenient while shooting.

Although there is no SWD in it, the focus is relatively quiet, fast enough, and always accurate. The lens does not rotate on focusing, so it's polarizer-friendly. The minimum focus distance is .2m, so you can get close to your subject with ok results and at 2.8, the bokeh is usually pretty nice - although macro is not what this lens is intended for at all.

I wasn't exactly blown away by the performance, but I wasn't really disappointed either. Sharpness across the frame is actually very good, nothing amazing, but more than satisfactory. It also remains pretty consistent through the most used apertures, so that's a big plus for me.

I have never had an issue with any vignetting. Lens flare is never an issue and extremely easy to control. Distortion is visible in certain applications, but not bad. I'd say average performance but it's easily fixed in PP.

Chromatic aberration is a slight issue. While it's generally fixable in PP, it's definitely there and becomes quite visible towards the corners. This is probably the lens' IQ weakest point. If you're shooting b&w though, which was often the case with me using this lens, it's a non-issue.

On to my subjective observations. Being locked into one focal range always lends itself well to creativity and practicing your framing, and 25mm (50mm equivalent) is a nice spot to be at making it versatile for what it is. I can take a walk around a city with just this lens and capture a wide variety of subjects, scenic shots, portraits, candids, macro-esque shots, even some action. Its focal range, small size, and acceptable focus speed allow for some fun street photography too. Considering what the lens will probably be used for, IQ is nothing to complain about. I do wish the max aperture were bigger.

It's a very affordable lens but despite it's good performance and relative versatility, it's not something everyone needs. Much more important than usual in considering this lens is your personal photography interests/habits. Depending on that, this lens may be just a novelty to almost a must-have.