To get the bad out of the way, I always worry about the resale value of a lens but a little more so with this one. You tend to get over it after the first download or two of your photos.
The good is that I am more impressed with this lens than I have beem with any lens below 85mm except for two macros I have. The macros hold their own but so does the 17-55mm.
I have a Tamron 28-75mm that is very sharp. I ordered a 24-70mm L lens and it could not compete with it. Very bad copy I had so I returned and had another sent to me. The new one wound up being a very good copy of the 24-70mm Canon and I was happy until putting it against my Tamron.
I keep my testing simple. I took 12 photos of my wife with the Canon L lens and 12 with the Tamron for a total of 24. I put T and C on the back of the best 12 photos (6 of each) and mixed them up. My wife put them in the order of most to least happy with the overall look, color, etc. The Tamron bettered the Canon and it was sent back the next day. I don't usually send a lens back but hopefully that was understandable.
Long story short, I did the same with the 17-55mm. I tested my Tamron and the Canon from 28mm-55mm. From the 12 photos, her first six photos picked were from the Canon, the last six from the Tamron. They were all close in my eye but there was a real world difference, enough for me to call the lens a keeper.
Hope you have the samr experience. All I can say is give it a go. It would not make it to page 3 on the B&S forum.