Ansatsu Kyoushitsu, AKA Assassination Classroom, has the sort of fun and silly premise that anime tends to become known for. It features on a classroom full of academically backwards students who are trying to kill their teacher--who is also a yellow smiley face with the body of a tentacle monster--before he destroys the earth at the end of the year. He can do it, too. He's already proved that by blowing a hole in the moon.
Assassination Classroom certainly has some fun moments, mostly related to Koro-sensei's personality and how his body functions. But these moments tend to get repetitive fairly quickly, and the flaws of the series threaten to outweigh them. The rest of the cast is fairly lackluster. This is likely a side effect of its Too-Many-Characters Syndrome. There is an entire classroom worth of students, all of them introduced in the OP, but only one or two are memorable. I can think of four off the top of my head: Nagisa, Karma, Ritsu, and that one dude who has something close to a character arc but not a good enough one that I can actually remember his name. The rest are just a blur of faces and names that have pretty much no real relevance.
What's more, the story doesn't often go anywhere. It is, as most shounen, deliberately drawn out so that the franchise can be milked for all it's worth. The result is that the plot largely becomes filler. Over the course of twenty-two episodes, we spend a bit of time learning how Koro-sensei functions and what his strengths and weaknesses are. The rest of the show is filled with Koro-sensei doing teacher things and the class combating other villains. These diversions would almost be welcome were they not a distraction from the real story. Sure, it's good that we're getting character development for these professors and students, but there are more pressing concerns. Namely, "why would such a cheerful creature threaten to destroy the Earth?" and "why does this creature want to teach a high school class?" I can ignore that the moon getting a big hole blown through it doesn't mess with gravity or tides. I can ignore that Koro-sensei can fly at mach 20 and is basically a giant emoji. But I can't ignore that the entire premise of the series is built on unanswered questions. The longer it continues, the more it seems like it's simply an excuse to create this specific situation. But instead of addressing these questions, we get a vague comment about Koro-sensei being a man-made biological weapon, then shrug off any other answers in favor of adding new villains so that we don't have to kill of Koro-sensei until sales start declining.
Assassination Classroom is a funny joke that drags on for about 15 episodes too long. Sure, the concept is fun, but a concept can't carry a show. There are too many characters for them to get fleshed out and the plot refuses to progress. What we're left with is a series with glaring questions that only become more frustrating the longer they go unanswered. And the worst part is that the show gives no indication that they're considering addressing them anywhere in the near future. Three stars.