Mega Man Zero 4 is surprisingly different from its predecessors. While the general gameplay remains, there are several changes to everything surrounding it. First, the Rod and Shield weapons are removed and replaced by the Z Knuckle, a fist weapon that lets you copy enemy abilities (it's quite fun actually). Second, the cast is greatly changed, with most characters from Zero 1 to 3 NOT returning (what even happened to Harpuia and co?). Third, sub-systems like the Cyber Elf and parts system are heavily modified, for the worse IMO.

In terms of level/boss design, I feel Z4 is a little behind Z2 and Z3 mainly since stages are pretty short and sometimes gimmicky. They're still good though.

Overall, this game is good but not as good as the others in the franchise. Still recommended though.