This game is better than Pikmin 3, and especially once you get near to, and reach, the post game content, I'd say it may get close to surpassing the first. For reference, 2 is my favorite.
The only people giving it a one star review are 3 Deluxe fans who liked the coop feature in that edition. But Pikmin was never really designed or balanced to be a coop experience. The whole point of the game is the efficient allocation of resources, a process or skill known as Dandori. You need to learn and plan how to put some Pikmin on a task and let them be while you set another task up with more Pikmin. Having two people run around greatly increases your abilities and would trivialize the campaign.
Frankly, if someone is giving it a one star review because there is no coop, it makes me wonder if they were fans in the first place. As far as I've read, most of the people leaving these reviews have only played 3 Deluxe, while long time fans love the game.
Onto some good points about the game:
Caves are back! These unique levels change the style of gameplay. Whereas above ground you are limited by time, underground you only have the Pikmin you brought with you. There are no ways to get more in large quantities.
The three Pikmin type limit is a GOOD thing. There are 8 Pikmin types available during the day. By limiting you to 3, the game makes the choice important. Also, if you just brought equal amounts of everything, you wouldn't have enough ice Pikmin to freeze most bodies of water, you wouldn't have enough blues to grab most treasures from under the water, you wouldn't have enough yellows to carry most out of reach treasures, you wouldn't have enough reds to reliably fight a fiery bulblax. See my point?
Frankly I could go on and on but I'd rather be playing it right now and doing this awesome post game content. Read the other five and four star reviews for an accurate opinion on how the game is, instead of Pikmin 3 "fans" who seem to want to sabotage the series by bombing the user reviews