Has 6-10 years of SLR/camera experience.
Super bright focus, beautiful depth of field, good 'feel' when focusing.
Only shuts down to F16, sticks out from camera body a long way.
Well, the obvious lens to compare it to is the standard F1.8 50mm! And I have both on my lap right now, on an A1 and an AE1.
The F1.4 is really quite beautiful - the outer glass element is bulbous and almost fills the 55mm filter window. You can see about 12 reflections in the glass, some a beautiful green and blue from the anti-reflective coatings.
The focus ring is 50% thicker on the F1.4 than the F1.8, and the actual action focusing is smoother, but also much heavier. Having large hands, I far prefer using the F1.4. There's also a little knob of plastic to which sticks out to the right of the lens when at infinite focus, so you can feel where you're focusing by touch.
At F1.4 the focusing view is super bright - you can focus in a pub / indoors with no problem.
Of course - the main thing is the photos. I've taken some really very nice ones at F1.4, where that extra 65% light really helps. With Superia 1600, hand holding indoor shots at night is possible with a little motion blur. And it's brilliant for dreary London in the winter with a more sensible speed film.
As to whether the expensive F1.4 is any sharper than the bog standard F1.8, I can't really tell - both seem to be a match for any colour negative film.
Now my standard lens.