Most keen photographers want at least one fast prime in their set of lenses. I've just bought this lens for my 500D, where it equates to a 135 medium tele lens on a film/full frame camera.
The lens is small and compact, not too heavy and with reasonable build quality. It doesn't have IS - none of the affordable primes in the EF range have this feature, and it's not much needed for short focal length lenses anyway. Just keep the shutter speed at 1/150 sec. or faster! The auto focus is very fast and accurate, and one shot full-time manual focus is available.
I've only had the lens a few days but I know what to expect - I had a fast prime for a film camera years ago! The major problem on film cameras was framing action shots - cropping slides wasn't really an option! - but with digital that problem has disappeared thanks to Photoshop. After a few trial shots I'm impressed - the lens seems sharp at all apertures. Background blur is great, but be very careful shooting wide open at close range - the depth of field may only be an inch or so. You may need to step back (with your feet!) or down with the aperture to get all of your subject in focus, and tweaking the manual focus will probably be needed.
The lens is great for portraits, but I'm itching to try it out on action shots - the fast/accurate focus and wide aperture will be an ideal combination. Those who only use zoom lenses just don't know what they are missing. There are situations - indoor sports, live theatre, gigs etc. - where the action-stopping combination of wide aperture and fast shutter speed available from a fast prime will beat the performance of most of the affordable zooms. I have an EF 70-200 f4 L IS - a superb zoom - but when the reach is adequate the prime will be far more suitable for low light situations.
My one niggle concerns the recommended lens hood (ET-65 111), and it's not the price. I have hoods for all my lenses, but this has an unusual pinch/pin mounting. It looks fragile, and sooner or later it will get the inevitable knock. I would have much preferred the normal thread mounting.
The bottom line is this is a very good lens - and a bargain at the price - and is sure to become my favourite lens for family portraits. If you think the focal length will suit you, just get one! Those with money to burn could opt for the EF 85 f1.2 - it is larger, heavier and has a whopping price tag of around £1700! For about 1/5 of that price, I am more than happy with this little beauty.