Prompted by a recent lecture @ Oxford University, by a researcher, it appears German SIGINT was partly successful in providing intelligence to decision-makers - yes one person didn't.

The key document is a post-WW2 report written by a German officer, Albert Praun, who in 1945 was Chief of Army and Armed Forces Signal Communications and wrote for the US Army:

His report was declassified in 1987 (according to the speaker) or in 2014 according to the document shown here:

An alternative and slightly easier to read is:

The speaker found that in 1940 British plans by General Montgomery to counter an invasion were fully known by the German SIGINT; one wonders when he knew this.

I have read an account of the German's success in reading the coded reports of the US Military Attache in Cairo, on the 'War in the Desert'. Plus references to breaking the USSR's top-level cipher machine. Both Rommel (in North Africa & Normandy) and Kesselrigg (in Italy) depended on SIGINT in the absence of air reconnaissance. Rommel lost his SIGINT unit in Tunisia.

What I had not heard before was that one arm of German intelligence (there were many) a research bureau run by Herman Goering from 1933-1945, was unknown to the Allies. It's main focus was internal security. See:

The post-war records of TICOM, 50k pgs held in the US National Archives, remain to be exploited and have been called 'the last great secret of WW2'. Yes, they were released to the public in 2015. See: