If done properly, collecting is the best structure for a platformer game. There has to be a reason to get you to go across dangerous platforms, or to do things you wouldn't normally do as you play through a stage. Having something to grab is the best way to accomplish this.
Donkey Kong 64 missed this point. There was basically five of every item, which required using all five characters to collect everything. It meant going back through the same areas five times over, doing the exact same stuff. Granted the characters had different moves, but this didn't really change enough to warrant the retreads.
Then there are things like Banjo-Kazooie, which had 100 notes that you had to collect in one run. If you mess up, you have to start all over. The levels are a bit too large for this, and the later ones have cheap deaths that make the process nothing but frustrating. This is one reason why I love its sequel, Banjo-Tooie, as it has none of that nonsense. Sure, it has more replenishable items, like all those eggs and feathers. But those are scattered around in bunches, and reappear after collection, so they're not a pain at all.
That said, I have such limited experience with Donkey Kong Country games! I can't really say if they use collecting effectively or not. That'll have to be my goal for the summer.