For most, like me, this will be a first move into L series lenses. It is like nothing you have used before, it out preformes my 20 year old nikon primes in resolution, contrast and colour rendition.
A few minor niggles though, for such well designed optics you would expect the casing and accessories to be well designed.
Lens Hood - very flimsy, nothing like the quality of the ones on their telephoto primes. Also would like to see a hood option for the 1.5 crop of dSLRs as an accessory.
Tripod Collar - perfectly rigid but too close to the lens barrel to use as a carry handle, hence it is always in the way for hand holding. Yes its removable but I use it enough to want to leave it on. It would be nice to see canon tripod collars being arca swiss compatible by default, it only takes two dovetail groves and would save a $50 plate. I suppose I just have to wait for RRS to design an expensive replacement collar.
Switches - biggest design flaw here, why not recess them. It is very easy to knock the AF and IS switches on or off when stowing the lens. It has become habit to check them every time I pick the lens up, though I still miss a few shots because I've knocked them.
Despite all these niggles, I would still recommend this lens as the first real lens anyone considered. I travel a lot and weight means I can not carry lots of primes. It may not be as good as some of the L series primes but it is so much more versatile. And if you cant get superb shots with this lens, it's probably not the lens thatís at fault.