Overall, I tend to agree with most of the comments so far.
Although, at least for chevrolet, the drop in power ratings (for 1971) was due to changing from gross ratings to net ratings. Ex: my 71 Vette with the base 350 rated at 270HP was the same as the 70 engine rated at 300HP. My '71 was a great car (after restoration) that I dearly miss. In 1972, the compression ratios fell and so did the performance, still I had a '72 Camaro that was fun to drive and it was a beautiful car.
There are other cars and trucks worthy of attention. I had a '76 LUV truck that was great. The little 4 banger was tough as nails and I drove the wee out of that truck on and off road. Took 3rd place (in class) at a local autocross with it.
While detroit struggled the imports took hold with cars like the Datsun 240/260Z, and the BMW 2002.