Why was the New Deal unconstitutional?
First of all, the "New Deal" was simply a campaign slogan FDR used to get himself elected in the first place. FDR's centerpiece of his new deal was the Works Progress Administration (WPA). There was another group named the Civil Conservation Corps which dealt with how land was used, specifically in the plains states. It is considering the most enduring of his plans.
The National Recovery Act (NRA) was declared unconstitutional. The NRA was not declared unconstitutional for the processes in wanted to put into practice, but because all power was held by the President. This was more a political move than a practical one and with a very conservative US Supreme Court, the republican party who feared FDR was becoming too powerful, used this as a ploy to make him less popular. That was in 1935 so you can see how well that worked out.