I am not going to pick apart the OP's post and try to diagnose the issue, but on face value, he expected the bike to be perfect and hopped on and quickly had a problem. Unfortunately, he was injured in the process. My opinion is that he should expect some sort of response from the shop and a little good faith tune up. Hopefully the OP has insurance and heals up. I would keep the two things separate and expect the shop to demonstrate on the stand that the bike now shifts through all the gears without throwing the chain and then send him on his way. It is then up to the rider to "road test" (carefully), and ensure that the bike is working as expected and considers it safe to ride.

The bottom line is to never trust someone else's work or to put blind faith into a shop before jumping on something as dangerous as a bicycle can be, and hauling down the road on it. The whole situation sucks but at least it was not worse.