It's on my T2i most of the time, and I believe the IQ is as good as any L I've got (except maybe the 135).
Outside, it's a star. I've found it to be nearly the equal of my EF-S 60mm for macro images. It does decent landscapes, excellent portraits and is just about a perfect walkaround lens.
Now, for indoor, I wouldn't dismiss it as easily as some. I've used it indoors a lot, always without flash. The 4-stop IS makes up for a lot of light-gathering deficiency. I customarily shoot people indoors at 1/30 at ISO as low as 200. Now, that's not going to help with motion blur if you're chasing a child around, but for normal situations, you can get away with it.
I tried a little experiment recently. For Thanksgiving, I shot all my indoor stuff with the 15-85. Usual late afternoon and night lighting inside a home. For Christmas, I used only a 50mm 1.8 shooting mostly at 1.8 and 2.0 (no IS, obviously). Well, the 15-85 dramatically outperformed the 50 in image quality overall.
Also, if you're going to have to buy a good flash, you're then in the dollar range of the 17-55 anyway.
Anyway, just my experience and thoughts. Good luck with however you go.