Quite subjective, many seasons have been interesting for various reasons. But I suggest 1978. The year Lotus stunned the F1 community with its innovative ground effects model 79 and sent the other teams scrambling to develop their own versions in a futile attempt to remain competitive while Mario Andretti "drove off into the distance". Brabham's response was the notorious "fan car", so effective it was banned after only one race. The year Renault, amidst much derision, fielded a tiny 1.5L turbo V6; it screamed like a banshee, produced amazing amounts of power from such a meager displacement, and exploded mid-race with monotonous regularity. The year Arrows scored their first GP points (despite ongoing litigation with the Shadow team over "stolen" chassis designs ...Shadow won, and Arrows went on to produce one of the ugliest F1 cars ever to compete), the year Williams first appeared as an eponymous team, and the year the colorful Hesketh team folded. Two unknowns made their first races in 1978 - Nelson Piquet and Rene Arnoux - and rising star Ronnie Peterson lost his life after a multi-car crash on the first lap of the Italian GP. The year Gunnar Nilsson, slated to drive for Arrows, was unable to participate due to ill health, finally losing his battle with cancer twelve days after the Canadian GP; he was only 29.
For me this technological variety made these years much more interesting than modern F1, which is rapidly approaching spec racer status.
And mention should be made of 1937, when the Mercedes W125 made over 600hp from a supercharged straight eight and could reach 200mph ...on skinny tires, wire wheels, no wings, and a six inch ground clearance. It would be forty years before F1 saw that much hp again.
