I bought the Canon 35mm f/2, and am not too happy with it.
I would be interested in why you were not happy with the 35mm f/2 (or anyone else who has used this lens)
I have read universally positive reviews on the 35mm f/2. Very good value for the price. Very sharp lens. Noisy AF is really the only consistent complaint?
It's a good lens, that has a few annoyances which make me feel uncomfortable with it.
Bokeh is one, and there's a photo (one with branches in the background, just the type of situation when the problem occurs) in photozone's review that illustrates it.
The manual focus ring and plastic finish make the lens feel like a toy, and the noisey AF doesn't help.
The lens has no USM, which forces a use of a switch to switch between MF & AF.
The lens has good IQ, but the Samyang has better IQ, improves on all those points (except for AF - it's fully manual), and is one stop wider.
Which brings me back to my point - Canon can fix those issues without redesigning the while lens or make it compete with the f/1.4 L. It's no more than adding USM, good MF ring, and better aperture (say add blades).
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A point I've missed is that Samyang lenses are sold with a hood and pouch. Canon sells pouches & hoods for non-L lenses separately, in this case for ~U.S.$50 in B&H. This is, of course, not a deal breaker, but it adds to the 'this is a cheap / toy lens' feeling.