Earlier this year, I had a client that asked me to make the transition to using ToonBoom Storyboard Pro. It was expensive ( about $1200Cdn) but in the end, I think it was worth it.
Despite a couple of minor excluded items, its a very function piece of software--the main selling points are that its functional for all kind of 'boards, can be used to create animatics......and, well...............its considered the industry standard now.
Yes, you can fudge around with other free packages, and achieve most of what Storyboard Pro does, but in the end......its one that "does it all".
I know of colleagues that draw in Sketchbook Pro and import into Storyboard Pro, and myself--I was drawing on paper and scanning/importing into the software, using Photoshop to manipulate.
I have not heard/read of any suitable free programs that offer anything close to the same.
BTW, I wish I could get away with 'boarding as loose as that Spiderman animatic you linked to. Too many clients are anal about models these days--and few let nice supple ruff drawing go through.
"We all grow older, we do not necessarily have to grow up"--Archie Goodwin