Anyone with experience with a Sigma 17-70 (Canon)?

[rmettier]

My basic 'everyday' lens is a Sigma OS 17-70 HSM Macro Lens for my Canon 7D. I bought it instead of the kit lens with my first DSLR and so far, I was quite happy with it. However, I've recently got a 50mm f/1.8 Canon and a 70-200mm Canon f/2.8 L Series lens and they are optically both noticeably better than the Sigma. Now I don't know what to think about my trusty old Sigma.

The 50mm is a prime lens, and I know that they usually wipe the floor with zoom lenses where sharpness is concerned, so I feel that's not a fair comparison.
The 70-200mm is in a totally different price category from the Sigma, and is known to be an excellent piece of glas, so maybe that's not a good measure either.

I'm torn. Is my Sigma just not that great and I hadn't noticed it yet due to lack of comparisons? Or is it quite ok, but I'm expecting to much from it? In other words, does it make sense to look for a better 'everyday' lens in the same price range as the Sigma? Or should I expect about the same from any 'reasonably priced' zoom lens in that range of focal lengths?

Anyone with experience with this lens? I'd value your opinion.

Edit: I borrowed a colleagues 17-85 Canon EF-S lens as a comparison and headed out early this morning to catch the sunrise on the old town buildings. Stayed mainly in small aperture, long-ish exposure land, trying to get a selection of different light/shadow effects and colors. Upon comparing the results, I have to say, the Sigma is certainly not worse than the Canon, and around the edges even seems a good bit sharper. They also don't quite agree on what 17mm focal length is, with the Sigma cropping a tad closer when fully zoomed out than the Canon.

I'll try out some close-up, wide open, shallow depth of field shots this evening. That, together with this mornings results should give me a basic idea of what I can expect from lenses in this price segment.