I don't know if difficult is the word I'd use, but I couldn't stand Pikmin 3, and I imagine I couldn't stand Pikmin 1 either, because of the time limits. I want to be able to take my time, strategize, and explore at my own pace. It ruins the fun to know that I only have 30 days, or that I'll lose if I don't collect X amount of fruit per day.
Pikmin 2 is so far the best game in the series, in my opinion. If I want to spend three days building up my Pikmin army and stockpiling the sprays, I can do it without worry that I'm running behind now. I don't need to rush through the game, and can take it at my own pace.
If only there were a mod for Pikmin 3 that removes the juice mechanic, or gives unlimited juice from the start.