I am a bit like you, I am looking for a prime 35mm since a while, and I am hesitating between buying the 35mm f2 IS now or waiting for a 35 f1.4 L II. I don't want to buy Sigma, and IMO the 35mm L v1 is more than due to replacement, it was made in the film era, and the tons of chroma and relative corner softness are signs of it's age. It's more than time for a razor sharp, chroma free, weather-sealed 35L, (maybe even less distortion); c'mon Canon, I know you can do it.
In the meanwhile, the 35mm f2 IS USM is probably the best offer from Canon, despite the ,IMO, un-deserved bad advertising around this lens. It's not L, but if you don't need 1.4, it's better than it's L brother with the added benefit of the IS. I don't think the built quality is an issue.
I had the original 35mm f2, for a while, I hated it and sold it quickly, due to its poor image quality (soft corners and awful bokeh), plus the cheap built of the original non L lenses (I still have the 15mm fisheye and the 50 compact macro (both excellent, once stopped down a bit), but they feel cheap and completely outdated).
My only real concern about the 35mm f2 IS is more about the vignetting that seem to be extremely high, and never completely disappears when stopped down; I know it can be fixed in post, but some reviews talk about 3 stops vignetting @ f2, that's a lot.
Plus I think it's still a bit overpriced for a 35 f2, even more if you consider the hood sold separately for 50$.
I will try to go this week in a store I know to make a few test pics. I anybody could comment about the vignetting, I would love to have opinions on that issue.