I agree, some of the enemies were pretty damn cheap or were near impossible to kill without losing Pikmin (Wollywogs and
Sheargrubs for example). Pikmin 2 improved this because it allowed you to kill the enemy and save the Pikmin being eaten, unlike the first game where even if you killed the enemy, the Pikmin would die.
As a matter of fact, the unlimited days was why I liked Pikmin 2 so much, because it allowed you to explore the area much more than the original. As weird as it may be, I'm on Day 124 in one of my Pikmin 2 files. You wouldn't be able to do that in Pikmin 1. Pikmin 1 felt more like one of those games you just sit down and beat the game in one sitting.
Don't get me wrong, I still like the first game, but the time limit was just meh and I believed Pikmin 2 expanded upon a lot of the concepts from the first while adding new ones. I could see why people liked Pikmin 1, it was a ruthless game where just the slightest mishap can ruin the whole day. However, I wouldn't mind them strengthening enemies back to their Pikmin 1 apeparances (Bulborbs, Blowhogs, and the Emperor Bulblax, etc) from when they were nerfed in Pikmin 2.