This drama probably won't work for everyone, so these are the points you should know beforehand:
1) The plot is formulaic because each episode has the same structure (alien wants to attack earth & earth defense squad has to talk the alien out of it).
2) The scenery is limited. It's literally all set in two rooms.
3) This is 100% a comedy. Nothing is really serious (on the surface).
4) It's very dialogue-heavy and I'm not sure how fun this would be to someone who knows nothing about the society and popculture of Japan.

That being said, I like this drama a lot. Here's why:
It's basically an insane comedy and while the basic structure is the same each episode, the drama still constantly managed to surprise me with insane ideas, whether it was completely outrageous aliens or things we learn about the members of the defense squad. All the actors were great and I ended up loving all the characters a lot.

What I also liked is that, as crazy as it is, it's a great snapshot on Japanese society. You have characters from different walks of life who all have their own issues (e.g. the guy preparing for the university entrance exams, the teachers who has to take care of his students outside school, the businessman/father who has to fullfill all kind of societal expectations). They are often selfish and then show compassion and humanity in the oddest situations.

Also, the whole situation is so ridiculously Japanese. You literally have aliens who want to eradicate humanity, but the main cast doesn't just kill them, they try to be polite and are busy juggling their private lives on the side. It's almost as if the drama is trying to tell us that aliens aren't scary in comparison to society and I think that's what makes it a great parody.