That's a mistake if that's his true intention, thought they hit a winning formula in A1 with a perfect mix of superhero action and comedy.
I don't think so at all. It would be a mistake to just run with the same instead of develop. The last film was a playground for our heroes. The main villains weren't much threat at all, if the team had been united from the start they'd have ended it long before New York.
The light tone matched the subject.
This time they're facing a greater threat and the tone will shift to suit as it should. This is Whedon so there will still be humour, it's not suddenly going to become MoS.
The trailer felt a little strange the first time I watched it. Second viewing it worked better. I think it may have been the sound.
I like it.