I love the Pikmin series just because it's darn fun to watch my brother play. But it's very heartbreaking when the Pikmin die. That's why I could never play it myself. Especially when you hear 'em splashing around, slowly drowning. Or when they catch on fire and they're running around they're slowly burned to a crisp. And in #1, you can't do crap about that, whereas in #2 you can blow your whistle and call your Pikmin to you before whatever natural disaster it is claims the lives of your poor helpers. Except for lightning/electricity. That' s instant death no matter which game.
We did play co-op a couple times in #2 and it was pretty fun, although the controls get confusing, especially changing the view. Oh man, after attempting it once for a few seconds, trying desperately to run and then aim correctly to toss Pikmin onto the enemy, being veeery careful with that because after you toss 'em your Pikmin are gonna stand around like idiots right in the path of said enemy -- after that, I never tried it again. Heh.
Okay, uh, I suppose I had some kind of point in all this rambling. ^_~ It is a good game, awfully cute and everything, great puzzles, though frustrating at times (but then what game isn't?). The controls will probably be your biggest enemy. I personally would stick with Pikmin 2, mainly because you have greater ability to save your Pikmin from water and fire, unless you have the mental strength necessary to not care too much, in which case you should start with #1. Can't say anything about Chibi-Robo as I've never heard of the game.