TLDR; Pikmin 4 is a good game, but it is not quite a good sequel, as it does not carry the themes of the previous games.

The Pikmin series is a compilation of real time strategy games where the player controls a captain who must survive on an unknown planet by utilizing tiny root-like creatures called Pikmin. The series plays as a sort of third person strategy game, where the player must hurry and get their goals completed as fast as possible, with time running out as the days go by.

 The second game does not do a great job of this, instead focusing more on combat, exploration, and resource management in the form of limited Pikmin in caves. The first and third games both have their own form of a time limit. Pikmin 4 has no incentive to play the game fast, at least in the main story. However the side mode titled “Olimar’s Shipwreck Tale” retells the events of the first game with the mechanics and areas of the fourth game.

The series has many themes but one of the main themes is the feeling of loneliness. In the first trilogy it is just the player and sometimes another captain or two with your Pikmin surviving on a hostile planet depending on the game. While there are not any humans, there are familiar objects like glass bottles, Duracell batteries, houses, as well as other household objects and locations. The main characters of Pikmin seem to be extremely small, around a third of the size of a Duracell D Battery, which enhances the attention brought to these items as they are much larger than the main character. This theme of loneliness does not carry into Pikmin 4, as the player has characters giving commentary fairly often. 

Throughout the series there are multiple protagonists. Olimar, the main character of the first and second games, shows up in every game in the series, and generally plays a role in the story, whether that is the player needing to save him in some way, having him be the main character. In the first and second games the player gets to know Olimar fairly well via his diary entries and emails sent to him, we learn about his wife and kids, and how much he misses them. This gives the player a reason to care about the time limit in the first game, so that Olimar can go home and see his family again. Pikmin 3 does something similar with an introduction that tells the story of how the main characters of that game are on an expedition to find a suitable planet with food to solve a food crisis on their home planet, and later on shows diary entries to show more of their characters. Pikmin 4 floods the game with a large amount of characters and that feels bland. 

The Pikmin series, of course, has many types of creatures called ‘Pikmin’, each one coming in different colors with different abilities, with the player to lead them. These abilities are typically just resistance to specific types of attacks or elements, for example fire, electric, poison, or even crushing! Some Pikmin types like Red Pikmin deal more damage, while White Pikmin move faster, and Purple Pikmin can carry objects with the strength of 10 Pikmin. In Pikmin 4 all of the Pikmin types return, other than Bulbmin. Pikmin 4 includes 2 new types, those being Ice Pikmin and Glow Pikmin, although you can only use Glow Pikmin using a specific item or in specific game modes. Some Pikmin feel less useful than others, however, they still have their uses.

One of the new additions to Pikmin 4 is a strange dog-like creature called Oatchi. Oatchi practically trivializes combat because the player can have Pikmin ride on it, granting greater mobility. Oatchi can also rush at enemies, stunning them while flinging Pikmin onto them. Oatchi makes many things that made the Pikmin series so interesting, those being the difficult fights and the clever strategies that could be used to beat enemies, unimportant and easy.

Caves first appeared in Pikmin 2 as long gauntlets where the challenge does not come from a time limit like most of Pikmin, but because of limited Pikmin. Every death matters in Pikmin 2, the challenge comes from conserving your limited amount of Pikmin. But in Pikmin 4, the challenge is lessened with shorter caves as well as Pikmin that can be found within these caves to replenish your numbers. Another downside to caves in Pikmin 4 is that players can return to any part of a cave that they have been to, without consequence. This essentially allows them to leave the cave to get more Pikmin, and return with a fully replenished army, there is no challenge. Although the caves are fun, they are not similar to any of the previous Pikmin games.

 In conclusion, Pikmin 4 is not a good sequel. It has many redeeming qualities, like its beautiful areas, fun puzzles, exciting caves, and a fun story. However, it does not have the core tenants of the Pikmin series, those being time management and resource management. I would recommend giving Pikmin 4 a try if you are interested.