I played season 1 for the first few weeks. Far as I know, none of the content got much harder although i certainly did not complete a full playthrough. I hit a point that I cleared an area, and when I went o go collect the beacon or whatever, I wasn't allowed because I wasn't the right level. That pissed me off because I was able to clear the content, but without any rewards at a lower level. Seemed like a dumb set-up.
Plus I knew the 6 week season reset was going to occur. It just pushed me off from playing more and I faded away to just not touching it at all. Knowing I would go back to a completely reset game/character gives me no desire to go back.
If they introduced seasonal content, but kept the main storyline progression as it was, I'd be fine. I can't be arsed to put in Hours of work each day to finish the story within their 6 week time constraint. It's dumb.