Summary: This is a great lens and costs a great deal less than others similar to it. Let's do the "not so great" first and get that out of the way. It isn't the fastest lens around and it has been around a while and could use an update...OK, that does it for the negative in my experience. Now for the good...and there's a lot of "good" in this lens.
Summary: I would strongly recommend it if you have a full frame camera like alpha 99. As you know 50mm you multiply with 1.6 for not full frame camera then your lens becomes 50 x 1.6 = 80mm - while on full frame 50mm remains as 50 mm. You need to keep a bit larger distance from the object. For Alpha 55 - like mine it is a good camera, but I would suggest you get a 24mm lens of sony.
Summary: I go out of my way to use this lens. The 1.4 aperture is a lot of fun and gets great shots with beautiful bokeh. I've shot a couple weddings and this lens is indispensable in low light settings. I haven't really had any problems with focus or aberration. I'll switch to this lens from my zoom and run around to compensate because the quality of pictures I get is so superior in color, sharpness, and versatility compared to my other lenses.