All 3 seasons are cleverly written, acted directed. They might not be perfect, but they are very very good. Season 4 however was the exact opposite. Boring, predictable, lazy writing, sometimes bad acting, or maybe just bad directed and a lot of plot holes. It's like a very bad, and weak remake of the original.

The only episode worthy of this show, from season 4, was the last one. This one is the only one, that really felt like black mirror. I really hope they'll do season 5 justice...if there will be.