Peninsula came amidst extremely high expectations for being the sequel of one of the best zombie movies ever. This movie is completely unrelated to its prequel, Train to Busan, so you can watch it even if haven't seen the first one. The plot follows another group who fled from Korea in a refugee boat to Hong Kong. Fast-forward 4 years, the surviving members of the group return to a deserted Korea to ransack the abandoned money. A task that should be easy, but Incheon is not as deserted as they thought it would be.
With a lot of action scenes and good visual effects, Peninsula failed in the casting of the support roles. The main actors are pretty good, but the acting of the foreigner (that is, non-Korean) characters is laughable. Also, parts of the plot and some actions scenes are highly implausible, to say the least.
However, Peninsula is still a very good movie, ranking high in the "Best Zombie Movies" list. It didn't live up to the expectations from Train to Busan, but perhaps the bar set by the prequel was just too high.