This is great stuff, all good exercises. Of course the 2 main things with any exercise routine is dedication and a good diet. Do this every other day and i'm sure your abs will be ripped.
Great form and instruction as always. I don't normally go as low as you but that doesn't mean your wrong. The main two things I tell people about this exercise is 1) Use your knees to get them heavy weights up, don't strain yourself trying to lift them up there or reduce weight just to get them...
I think your form is fine and the weight seems reasonable, you got a few good reps out. With regard to the last one I didn't see too much problem for your shoulder, so long of course as it doesn't hurt. To stop such 'hanging' when reaching failure you could try not going down so low on the fina...
Like the form, not so sure about putting it down every rep but can't do any harm.