Phew, glad I picked up a copy when I did a month or two ago. I was looking to get a new Wii U game after beating 3D World and was looking at Pikmin 3 and a few others. Pikmin 3 was the only one that was actually a little difficult to find, so I figured I better go with it over the others just in case.
Interesting.
I still haven't opened my copy. I want to play the first two games, and I dunno if I should just start from the beginning. Woe is me, etc., etc.
They're all pretty similar from a gameplay perspective IMO, so you're not missing much is you skip any.
Pikmin 1 has a 30 day time limit to the game which some people love for the added tension, but I wasn't a huge fan of it.
Pikmin 2 removes the overall time limit, added dungeons to the game, and a second character (to help with multi-tasking). You're also collecting some real world objects in the game (like Carmex and Duracell batteries) which I find pretty charming.
Pikmin 3 obviously looks the best overall and adds a third character for your team, but it seems to have removed the dungeons (haven't beaten it yet, but it seems like they're gone). It adds an overall time limit back in the form of the amount of juice you have left, but you end up getting so much fruit it becomes less of an issue pretty quick. Boss fights seem to be a big improvement overall too (but I haven't played them all the way through yet).
I haven't beaten any of them yet, but have played a lot of each of them. 2 is my personal favorite since I can play it completely at my own pace and take time to explore without any worry of wasting time. It's just the pace I enjoy for this kind of game and it seems to have a ton of content.
3 is still very very good, but it made a few core changes to the gameplay of 1+2 I'm not sure I prefer. You used to be able to guide where you want all your Pikmin to go; a little song would play and they would move around in a circular direction you move the wii remote (or c-stick) in. 3 lets you lock on to stuff and send all of them to attack at once, and there's a dodge roll you can get, but I miss manually guiding of them. I still haven't fully embraced multitasking with the 3 characters yet which seems like a good way of getting a lot done in a short time, but it doesn't seem like a requirement for the most part.