Reading further up this page, it looks like you did know about him leaving but forgot in time to be surprised
And I agree actually, my binge of the first two seasons was glorious. The fast pace of the show is just further accelerated with a binge watch.
And I think the quality significantly improved as early as episode 3 with Wells' shock death and everything going full Lord of the Flies in the aftermath,but yeah it's come a long way from then too. It's a shame this show has the "typical CW teen show" reputation with people who never gave it a chance or bailed early because it's so much more. Beyond a few characters with seemingly impenetrable plot armour (which plagues almost every show tbf), it's a rare show where I really feel like the stakes are constantly high.
And of course mass tragedies like the Culling and the Mount Weather massacre that you'd expect to be averted at the last second (the latter especially because they're not gonna have the main heroine of the show be forced to commit genocide against mostly innocents... oh yes they are).