Pikmin 4 is a love letter to the entire Pikmin franchise. I wasn't expecting much going into this game, and after the demo, was expecting the auto-lock-on mechanic to ruin my playthrough. While I still wish there a toggle for that auto-lock-on (so it would be closer to Pikmin 3), it doesn't actually get in the way as much as I thought.
But seriously, this game brings back so much from the older titles, and mixes them in a new way that is unique from them all. Pikmin has never really been a consistent series. Pikmin 1 was short and sweet, time-limited, a bit jank and easy to learn, but hard to master; Pikmin 2 did away with the time limit, and was pure and utter challenge mode, could be a cake walk with the right strategy (purple pikmin or bitter sprays) or an unfathomably difficult mess; Pikmin 3 went back to being semi-time-limited, and drastically reduced the difficulty, but introduced some incredible quality of life controls (including three captains, throwable captains, and go-here commands, allowing for infinitely more strategy)
And now, Pikmin 4 goes back to being non-time-limited, and adds so many new tools and mechanics, including a drone to pause time and survey the area ahead, an idle pikmin round-up whistle, and poochie, a playable and upgradeable half-captain, half-pikmin hybrid, which has even more versatility than Pikmin 3's captains.
The difficulty is a bit on the lower side, for experienced players, but as always, can be pretty tough for newcomers. Poochie charge with stun and a bunch of Pikmin (particularly the new icies) can usually kill most enemies within seconds, including some of the tougher bosses from the older games. It's not that previous enemies have been nerfed, but just that there are so many tools introduced in Pikmin 3 and 4, that negate a lot of the difficulty in the original game. The ability to just charge winged Pikmin into spider bosses, negating their stomps; or throwing bomb rocks whenever you want at emperor Bulblax for the easy stun; or using rocks to cheese empress bulblax; there are many tools that can trivialize combat, IF you know about them. To me, this is not a bad thing, but I can understand how masochistic Pikmin 2 players would prefer to have less options, in order to have more difficulty.
There are a few minor complaints, such as the amount of forced dialogue (particularly when picking up or turning in quests), and some poor menu navigation, but for the most part, the gameplay itself is as fun as it's ever been. And it's always a treat to find a classic returning enemy, or a familiar cave layout; this game is just a treat. It won't replace any other Pikmin game in the series for me, as I enjoy them all for what they are; but this game is definitely good enough to stand alongside them.
Oh, and the lack of coop campaign SUCKS. I would have preferred a coop experience after the amazing Pikmin 3 coop, but Pikmin has generally been a single player experience for me, so I can't fault the game too much for what I wanted from it; I'd rather judge it based on its own merits.