Have a look at Scott M's images. This is what the Canon 17-40 is all about.
If you want to compare specifications, look at distortion figure, pixel peep etc then this is not the lens for you. If you just want to produce beautiful images with stunning colour rendition the 17-40 is one of the best. I suspect that Scott M has done little processing with that first image. In my 9 years of using my 17-40 this is what I came to expect if the light was right, as I say the colour rendition is superb on this lens.
True the 17-40 is not the sharpest tool in the box and it does distort quite a lot at the short end, but these are aspects of the lens that can be corrected (in the case of distortion) or better still used to your advantage. Photograph a whole car with the 17-40 from a low angle at 2 feet - very eye catching to say the least.
There is a fly in the ointment (there always is!) and that is the Canon 16-35 F4 L IS. It is a "better" lens in almost all respects and I am happy that I traded my 17-40 to get one. However that doesn't degrade the 17-40 in any way. Although it's specs and theoretical performance don't look good these days, just try one and I think that you will be very pleasantly surprised!
If the Canon 16-35 F4 is within your budget then I would say go for that lens, but if it isn't then the 17-40 is still a VERY viable lens and (in my opinion) fully it's equal in many circumstances - but not all.