@stevey – I’ve definitely had the experience of a level seeming easy the first time through, only to becoming an exercise in pulling teeth on later attempts. “Easy” may also be a relative term compared to how hard the game gets later on. I don’t think college was easy, but it probably would have seemed easy by comparison if I had gone on to grad school!
Another thought is that we might have had our birds leveled up to different degrees when we first reached a level. I’d imagine a new player just starting out now, who didn’t have to wait for the release of new level sets and who wasn’t playing the Arena in the meantime, would have a harder time finishing some levels with lower-level birds. Whether just playing through the levels should get your birds up to a significant enough experience level to make things reasonably challenging, but not painfully so, or whether you should have to go back and “level grind”, or play the Arena a lot, or bribe your way to victory with real-world cash, is up for debate. (I’m not a huge fan of any of the latter options, though I do enjoy replaying the levels and the Arena just for the better understanding of the game I usually get out of it.)