I was very sceptical when I purchased it, after reading all the bad reviews.
Being a happy amateur, it did take some time learning to use it (and I still have my fair share of misses), but the "hits" are just beautiful pictures.
The 50L "creates" light, the pictures have more vivid colours than what's there in real life, and the pictures are tack sharp from around f/1.8.
I have not noticed any backfocus issues on my 5D.
For me personally this focal length is perfect for most situations. Paired with my 135L, I feel equipped for everything.
It's well built, but not too big and heavy.
The price in my country is... too high. Despite that, I don't regret upgrading from the Canon EF 50mm f/1.4.
The 50L helps me to be a better photographer. I love it!