I wasn't keen on Crash 4. I appreciate they were trying to do something different, but whacking up the difficulty and having to scrap the lives system to compensate just felt lazy and disappointing. Striking a reasonable difficulty balance is one of the main challenges in game design and to me, they failed it.
I think Crash 2 was about the sweet spot and what they should aim for. Once you got good, you could sort of flow through the levels smoothly.