Mega Man X4 was originally released by Capcom in 1997 on the PlayStation and Saturn, 2 years after MMX3, and 1 year after MM8. Like Mega Man 3 and 7 were to the original series, Mega Man X4 was a big turning point for the X series. Most notably, it featured a completely new graphical style and it was the first game in the series to let you play through the whole game as two different characters. Mega Man X4 is available on PS3, PSP, and Vita as a PSOne Classic, and it's one of the games included in Mega Man X Legacy Collection 1.
In Mega Man X4, Sigma persuades the robot army known as Repliforce to turn against humans and then drops a floating city on another city below, killing millions. X and Zero then set off to find answers, because they're basically robo cops. They play up the Maverick Hunters being the police angle a little more in this game. The story is not great, but the presentation is pretty awesome. Like in Mega Man 8, fully voiced anime cutscenes play at key points during the game. There's even different cutscenes for X and Zero’s games. There's also different dialogue between you and all the Mavericks that will play before boss fights. They really try to keep the story in the mind of the player throughout the game, and that's cool, but it's just not an interesting story, and the new characters feel pretty throwaway, like Duo in MM8.
There a much more interesting subplot going on in the game, though. It’s vague, but it reveals some of Zero's origins and hints at what happened to the original Mega Man. X’s ending also hints at the events that could potentially set up the Mega Man Zero series. These mysteries might never be fully explained, though, since that would probably mean putting a real end to the 2 series.
My favorite thing about MMX4 is being able to play as either X or Zero. It’s almost like getting 2 Mega Man games in 1. They have the same basic moves, like jumping, dashing, and wall jumping, but their weapons and upgrades are completely different. X plays like classic Mega Man X. He has his arm cannon, the weapons he gets from bosses are mostly long range shots, and he can get armor upgrades from Dr. Light’s capsules, which give him new abilities, like the air dash. He gets a few new tricks, like the air hover ability, but he's still the same X we know and love.
Zero brings a completely new gameplay style to the series. Zero is a melee character, and all the weapons he gets from bosses are more like moves you’d get in a Metroidvania than the usual Mega Man weapons. When Zero beats a boss, he gets new sword moves he can use with different button combinations, such as a shoryuken-like rising flame sword move, and a downwards thrust that turns his sword into an icicle. Instead of getting abilities from Dr. Light's capsules, Zero gets new traversal abilities with some of the boss weapons, like the double jump and air dash. Zero was made by Dr. Wily, so Dr. Light wouldn't have made anything for him. Zero also has access to all his moves at all times, unlike X, who has to switch between weapons.
What set the level design in MMX1-3 apart from the original series was the emphasis on replayability and exploration. MMX3 went a bit overboard with this aspect. MMX4 really dials back the amount of hidden items and exploration, though. There's still hidden E-tanks and heart tanks, and you still have to use boss weapons to get to some of them, but a few of them are in plain view or don't require any special ability to get. The level design feels a little closer to the original series’ as a result. There's less exploration than in any previous MMX in this game.
I think the Maverick bosses in MMX4 are some of the best in the series, especially when playing as Zero. Mega Man bosses usually feel like pushovers when you use the right weapon, but I actually had to pay attention and learn patterns here. The final Sigma fight was definitely the most challenging fight in the X series up to this point, and probably harder than any Wily fight, too. It's a 3 phase fight with 2 things to kill in the final phase. The final one is pretty demanding in terms of memorization and execution, too. Since X and Zero play so differently, most fights require very different strategies for each character.
Both the art style and in-game graphics got a pretty big overhaul for this game. It looks like they were influenced by MM8’s style. The character designs are a little more anatomically correct, with longer legs and smaller heads, and the levels have that same camera angle that shows the floor and gives the environments a more 3D perspective. All characters and enemies have a lot more frames of animation than in the SNES games. Zero looks especially impressive with his luxurious ponytail flowing in the wind as he jumps around. The environments all have very detailed sprites with lots of animations, like flowing water, ships flying in the background, and pulsing lights on the machines the artificial nature has been built on top of.
I love this game’s soundtrack. It's a huge improvement over MM8’s. It sounds like Mega Man music with a hint of 80s synth pop. The instrumentation used in the Maverick level’s themes are all very fitting and instantly invoke images of each environment. The voice acting is very bad, but it has become retroactively great, thanks to such ridiculously bad lines as Zero’s “What am I fighting for!?”. Sadly, the volume is all messed up in the MMXLC version and the VO in the cutscenes is way too quiet.
Mega Man X4 is one of the best games in the X series. It’s right up there with X1 and X2. I think it’s pretty amazing how the level and boss designs works so well for both X and Zero with almost no changes. I love the music, graphics, and animated cutscenes, even with the bad story, and how it finally gave us the playable Zero we had been waiting for since X1, without the limitations of X3, and that it made multiple characters a standard feature in the series. Mega Man X4 is a must play for all Mega Man fans.