I like DeNiro but I read somewhere that there are a lot of people that thought it was a mistake for him to play two parts in the same film. I haven' watched this but did notice that I have access to it, maybe I will change that and find out for myself.
I've read someone asked in a review "what's all this hatred due to playing both roles about", that's how I know there must be people not happy about it, but haven't read a single comment why.
Honestly, I don't know why people think it was a mistake. It's a possibility, an opportunity, it's something different than just playing one role, but each to their own.
I hope to read your review on the movie. Give it a try.