It's not as good as it could or should have been. If you don't know much about Chernobyl, it's worth a watch. If you do know a fair bit, it has a lot of exposition. It is not an action show.
I don't think it is a snooze fest like zombie is saying. Others complain that it is a British cast playing Soviets, which is kind of a dumb grievance. Seems to be taking an obvious anti-nuclear power stance, which I find somewhat misinformed, and too easy.
There are better places to get info about Chernobyl, and there are better dramas. I'll watch it out, because it was an important happening. But it could have been a lot better.