Season 1 and 2 are perfect if you want a fun (yet sometimes tense and steeped with mystery) plot, and personally I truly enjoyed season 3 purely for the characters. The actual plot of season 3 can be a bit weak, but I look at it as more the Hargreaves siblings (+Lila) having a weird week in a hotel. But honestly, I hated season 4. The writing was terrible, there was zero character development, and the ending to an otherwise good show just felt butchered. I would still watch the show again and will likely do some rewatches, but I'd recommend skipping season 4 entirely.