Gordon has written a book ... in case you want to read a really long book ... The Rise and Fall of American Growth
But you could just read the papers the first piece and the sequel.
Basically he is suggesting that recent innovations 'tech' have not been as good for the U.S. as previous ones (electricity, internal combustion engines etc.). Good ... meaning in terms of productivity and economic growth. So the growth rate of output per hour was 2.36% p.a. over the period 1891-1972 and 1.59% from 1972-2013. Did computers etc. make no difference? They did, but looks like diminishing returns may have set in. The same statistic (rate of growth of labor productivity):
1972-1996: 1.38% p.a.
1996- 2004: 2.54% <<<< here is the spike
2004- 2013: 1.33%
Hal Varian's consumer surplus argument does not cut it with Gordon (and rightfully so). Varian says many of the 'new' tech innovations give us more consumer surplus and consumer surplus is not part of GDP, so that's why things don't show up in growth statistics. Gordon says consumer surplus was never part of GDP.