I am a big fan of small variants on core mechanics in games. I have like a bazillion of ideas like this. I haven't played Tetris effect either.
But I agree about the summer, too much of them are changing. Also, the worst possible thing happened in my design, which I didn't know how to go around. The fact that the Fall comes after the Summer. So, after the summer leaves you with a total mess, the fall comes with a speedup, and then the Winter comes without the ability to slide pieces in. So, yeah, the seasons are thematic, but then again, not kind towards the player.
But of course, there could be other interpretations of the particular season, or I could activate only 5th season (so that at most one season per year has an effect applied).