Yes I did. It made absolutely NO sense whatsoever and I was rather annoyed because I sat through the credits waiting for it in spite of having to pee REALLY bad. :mad (I had a TB special. I really ought to know better...:ninja)
TB special?
As for the scene at the end of the credits:
From the movie we can see and infer that Loki has numerous ways to travel between worlds etc. His falling into the nothingness didn't mean he was dead although the movie kind of implied that. He's an evil barstool and wasn't doing that out of some 'woe is me, I've lost and now going to kill myself' He was controlling the scientist too and no doubt manipulating events to try to use that power source for his own ends. That power source being something similar to the 'all-spark' in transformers. Cosmic Cube is the name for this thing but who knows what they'll call it in the next movie.