This review is of the English dub, but most elements discussed should stay true regardless of which language version you watch.
Warning: Professor Pain involves adult oriented themes such as violence, suicide & terrorism and is not appropriate to young audiences.
Professor Pain follows the titular Professor Ohse during a hostage situation of his orchestration at his workplace Aoi College.
The runtime is fairly short with only 2 episodes á 30 minutes.
As the story progresses we get to know the main character, his motivations and his past through the events transpiring and past events shown as flashbacks. The character starts out menacing and mysterious in the early scenes,
but as his backstory is fleshed out and explained we can start understanding him.
This leads to the story overall going full circle, making the character's choice of actions understandable and through that the story can easily be made sense off without major holes.
The exception to this is the many side characters. They do not have the privilege of being the center of attention storywise, and do not get the screen time needed for the viewer to really get to know them. This makes their behaviour hard to understand and sometimes erratic, because we never get any insight in who they really are. This is largely because of the short total runtime, and a few more episodes would have helped this out profoundly.
The artstyle is concise and follows the same standard of quality throughout the whole series. The animation is very fluid with the exception of the last frames, which alternate between art frames and black narrating frames. This change of pacing looks somewhat outlandish when compared to the rest of the show, but still manages to encompass the final events transpiring.
Sound and voice acting is very immersive and the English version has a fairly last cast of voice actors, most performances are not very remarkable, but also has very limited amount of dialogue, so there's not much opportunity for it to shine. Looking at it from the opposite view, there's none of the voice acting that stands out as being particularly poor, it rather fits the dialogue very well and immerses the viewer completely. A couple of the more comedic lines are exceptionally delivered and needs to be commended.
To summarize, even though several of Professor Pain's aspects aren't outstanding, but merely average, there's nothing that stands out because of poor quality. This combined with the voice acting often giving great delivery of the dialogue makes Professor Pain a very enjoyable watch.