Firstly, I do not think the "Death Cure" does follow the stereotype of a teenage basic movie, in which probably a all romance between Thomas and Teresa would happen during the entire saga. Actually, the film creates a strong story meaning of friendship between this entire group that started as strangers that had to learn how to trust eachother. It's not just like any other teenager movie, like the hunger games or the divergent in which this kids are destined to compete and kill eachother. In this movie though, this group of young people fight and look to find a solution (by not torturing teenagers) for a possible real life situation (apocalypse) and a serious problem that the world is dealing with in that moment.
Secondly, I understand the point that you think Dylan O'Brien acting is mediocre, however, for an actor who has never been to an acting school, I think he has developed and progressed alot ever since his first role in Teen Wolf. So don't just criticize his acting abilities, for not expressing well, because his role has a very complex persona to interpret (and never forget...he is still learning).
Secondly, I understand the point that you think Dylan O'Brien acting is mediocre, however, for an actor who has never been to an acting school, I think he has developed and progressed alot ever since his first role in Teen Wolf. So don't just criticize his acting abilities, for not expressing well, because his role has a very complex persona to interpret (and never forget...he is still learning).