I thought long and hard before purchasing this lens and sold a lot of gear to get it. It's very hard to 'try out' lenses here in the UK so I bought it after just a very brief trial at a CPS event locally.
After a month or so of use, I'm amazed by the IQ of this lens - that's the first thing that strikes me, having been a bit frustrated by the 16-35 I used to own - itself a very good lens but with the 17TSE I can get amazing detail with subjects near or far. And that's before you consider the ability to tilt/shift. So far I've had little need for much tilt as the DOF is brilliant as is. Shift is much talked about for architectural work but it can also be invaluable for landscapes - particularly where towering cliffs are involved.
I've been pleasantly surprised by how little I've needed to clean the glass to date and also how controllable flare seems to be with a little shading from your had, a bit of cardboard or similar.