I've not used 3rd party lenses before. How do they usually stack up against OEM? This is an interesting lens to me. Can't wait to read more reviews about it.
Generally, I avoid them, but the Sigma 35 F/1.4 is being widely regarded as a game changer for Sigma's future prospects. From Roger at LensRentals:
"It’s been a long time since a take was so easy. This is the sharpest 35mm made. It costs a lot less than the Canon 35 f/1.4mm or the Zeiss 35mm lenses. Any questions? It’s extremely well built and everything I’ve been able to see, inside and out, indicates quality control has really improved at Sigma.
If you’re a bokeh fanatic, you may like something else better (or maybe not, that’s a subjective call). If you need Image Stabilization, then the 35mm f/2 IS may be worthwhile. Otherwise, this is the 35mm lens.
Arguably as good or better than anything else made, and at a lower price."
That lens also won a rather odd fan-voted blinded study on best bokeh on DigitalRevTV -- they posted three shots without saying which lens was which (no EXIF data posted), and the fans chose the Sigma 35 over the Nikon and Canon.