I wasn't until Whedon took over, and is changing a lot of things. The original Avengers was supposed to be crap, and he re wrote and fixed it. Avengers 2 had too much interference and was very mediocre. Good to watch once, but nothing I'd try to see again. If he is given free reign to fix the Justice League, I think it could be good.
I do like the casting, I like Cavill as Superman, the guy doing the Flash could be good, I liked Gal as Wonder Woman, Khal Drogo as Fish Guy, and I actually like Ben as an older Batman.