Cortex Strikes Back is a very solid game. The controls and physics are excellent and make Crash's moveset satisfying. The jet board is just ok and the jet pack is pretty awful but that's only 2 levels and one boss fight. It's a bit too easy imo, even completing the game 100%, but it is far from boring.
Crash 1 is rough on the controls but the levels work well with the simplistic moveset, and earning the gems by getting all crates without dying provides a good challenge. Its only real issue is the save system. I enjoy it as much as Crash 2.
Warped has too many shitty vehicle levels and the new powerups removes any challenge the game has to offer since you can just slide -> double jump -> tornado in the most dfficult levels. Even Future Tense from N.Sane Trilogy was too easy because of this. It was my favourite when I was a kid but today I just don't feel like playing past N. Tropy.