I've used the 14-54 for quite a long time, for everything between press, landscapes, portraits and general recreational use. I'll try to sum up my opinions on it here.
Let's get on with it!
Build is, frankly, one of the most important things with a lens. My dad used the OM system back in the 70s, and I've taken over his old primes and his old OM-2. Let's just say that I think they've faired a lot better than most of todays lenses will have in 30 years.
The 14-54 though, I think should last just as long. It's built very well, feeling solid, firm, both focus and zoom rings moves very smoothly. For those accustomed with lenses like the 14-42, there is more resistance in the 14-54s zoom ring, but it has a much more satisfying feel, being better damped and in my mind, more responsive. The focus ring is smoother than the 14-42, has more resistance, is also better damped and works better for MF.
Compared to lenses like the EF-S 18-55 and 18-55 IS, it's of course a much more satisfying product to hold, while the Nikkor 18-70 is about the same build, but a tiny bit under it. L lenses are on par or better, but this is only Olympus' High Grade lineup, not the Super High Grade.
I'll also note that the lens is weather sealed, and will give very good resistance to the elements when combined with an E-1 or E-3.
The lens balances well with the bodies I'v tested it on (E-400 and E-3). It is light and compact.
The front element does not move during focusing, but the lens does extend during zooming.
Lens hood comes with as standard, tulipe shaped. The lens is also supplied with a pouch made out of artificial leather.
Image quality is essential in this price range of lenses.
It is tack sharp at all apertures and all focal lenghts, with a sweet spot at f/5.6 and around 25mm. Of course, below f/11, diffraction kicks in. Keep it between f/2.8(3.5) and f/11, and you'll be happy.
Contrast is nice, and bokeh is mid range. I've seen better (the Panleica 14-50/2.8-3.5 for instance). The bokeh isn't perfect, but it's not too much of a bother.
As for distortion, there is some.Specifically at 14mm, it can be noticable, but it's no worse than I've seen with other lenses from other manufacturers.
It is possible to see slight vignetting at f/2.8 and 14mm when photographing a totally white piece of paper, but it is not anything you will notice in practical use.
CA is not an issue to my experience.
The 14-54 is a standard zoom, comparable to the likes of 17-55 from Canon and Nikon, and the 16-50 from Pentax.
Compared to 35mm, it's a 28-108, which is quite good. The EF 24-105L has better WA on 35mm, but it's also a lot bigger. I'd like a 24mm efl WA in the wide end, but then again, there's the 12-60.
It focuses relatively close, it's not a macro by any means, but if can focus very close.
I've already mentioned the 14-54 being weather sealed.
It's a con in my mind that it's variable aperture, this can be irritating, but for me, it's not a deal breaker.
AF is good in good light. It focuses fast and accurately. It's not good enough in bad light, but this has more to do with my E-400 than the lens, on the E-3 it's supposed to be a lot better, and that's also my experience when I had the chance to try it on an E-3.
Value for money
It's very good value for money. They're cheap new, but can be had for very small sums used. It give 28-108 millimeters of high quality glass with decent speed, well corrected and without any crucial problems regarding optical quality.
+ Excellent build
+ Weather sealed
+ Front element does not move during focusing
+ Very sharp at all focal lenghts and all apertures in the range f/2.8-11
+ Well corrected
+ Little to no CA
+ Little vignetting, a non issue in real life
+ Good contrast
+ Good range
+ Focuses close
+ Good AF in good light
- Variable aperture (2.8-3.5)
- Slow AF in bad light (mostly related to the body)
- Noisy when the lens focuses through it's full focusing range
- Mid tier bokeh, could be better.
- 28mm wa is a bit narrow compared to lenses like the 24-105 on 35mm, 12mm would be better (but there is also the 12-60, after all)
As for sample shots, I'll try to do a comparison with the 14-42 during the weekend, and some 100% samples at different apertures, and a bokeh demonstration, but right now, I can't be bothered.