Zero 1: This game made interconnected maps, things that we won't see again until ZX, in my opinion it has the most difficult final boss.
Zero 2: Returning to the classic format of choosing stages or missions, the difficulty decreased compared to Zero 1.
Zero 3: The longest of the tetralogy, we continue with the classic level choice format and are introduced to the true villain, also the cyberspace was a easy mode for stages.
Zero 4: The worst for me, despite its attempts to innovate by changing the climate in the stages. I didn't like grinding crystals to make my elf more powerful.
ZX: We return to the interconnected map designs, but with a map that was totally poorly made and almost impossible to understand, getting lost was very frustrating because of that, of the forms they give us only ONE is really good, the rest are just gimmicks.
ZX Advent: Now, if you can navigate and explore the map well without getting lost or frustrated, copying the boss forms is totally useless and a gimmick as always, only the ZX form is necessary to pass the game well. But in general there is a substantial improvement compared to the previous game.