Although Zero 3 is objectively the best in the series (or even the entire Mega Man franchise), this game has always been my favorite. The music is more memorable than that of Zero 3 in my opinion (especially Straight Ahead and Esperanto), and I personally like the new elf system as it makes it utterly impossible to permanently screw your rank. Speaking of which, in this game you don't need a good rank to gain EX skills! Yay! Instead you only need to adjust the weather to "hard," which is a much less frustrating endeavor. One of the best parts about this game is its story. A problem that plagued the entire X series and the Zero games before this is that the motivations of all the major characters (such as X and Zero) are centered around the protection of human society. However, we never actually see this society in those games. Zero 4 introduces the perspective of a human caravan escaping Neo Arcadia during the tyranny of Dr. Weil, the villain in this game (as well as Zero 3). The way the story highlights the conflict between humans and reploids is done exceptionally well. The ending is also amazing but I won't spoil that here. The only problems with this game is that elemental attacks are permanently bound to EX skills and cannot be connected with charge attacks like in the last two games. The parts system is also a nuisance compared to Zero 3's but using an online guide can help. Thanks for reading this :)