Weapons or parts. Neither are outright required, it's a matter of what tickles your fancy. That's why I love the game.
So..do we all agree that this game is an unenjoyable chapter of Megaman history?
ABSOLUTELY not. For all of the ambition that X5 showed, X6 pretty much perfected everything it attempted (other than the armor-must-be-completed-before-use thing, dunno what they were thinking with that one). X6 is one of my favorite main-series games, right up there with X1 and X4.
arguably mis-balances X and Zero's abilities
Holy hell, is that ever burying your head in the sand. All of the game's "standard" forms (Falcon, Blade, Shadow, Zero) are balanced according to offense, defense, and mobility (mainly in mid-air). Falcon is the all-arounder without excelling in anything in particular. Blade is more mobile, less offensive. Shadow is more offensive, less mobile. Zero is both offensive and mobile at the expense of defense.
Beyond that we have the cheat code unlocked Ultimate Armor and Black Zero which both excel across the board, and plain vanilla X, who as previously mentioned exists for no reason other than challenge.
It's also worth mentioning, as far as "balance" goes, that this is the *ONLY* PS1 game where the Ultimate Armor is not "abilities you already had + infinite Giga Attack". I still don't get why X5 didn't just give 4th Armor the Stock Charge...
The developers of Mega Man X6 just said "[tornado fang] it" and decided to make the most difficult, frustrating, cheap, and unfairly punishing Mega Man game of all time.
While X6 does pretty much throw the kitchen sink at you, I don't agree in the SLIGHTEST that it is unfair (well, besides maybe Mijinion's nightmare effect). It is more open, and expects you to think for yourself, and the solutions run considerably deeper than the formulaic obstacles that the other games present. While it presents tremendous challenges there's also a wealth of work-arounds to its many challenges, which engages the player by having them find *a* solution without it necessarily being the only arbitrary strategy that the developers just decided should work. Further, the game takes what X5 attempted to do with the expansion to armor and parts, adds more to the mix, and unlocks its full potential in a way that X5 simply does not allow. The increased difficulty is the natural evolution to continue to keep the game balanced in the face of all that power. Otherwise, you get Xtreme 2 (which I also love, but not everybody likes easy games).
As was said above I too get that X6 isn't for everyone. But the things it does differently are an extension of what Mega Man is built on: non-linear progress, growing more powerful, and finding the best weapons and equipment to tackle a given obstacle. They were simply taken to a far greater extreme than ever before (or since). To me, that is challenging for all of the RIGHT reasons. Unfortunately, it also makes the game less approachable, both to outsiders and to the not-so-hardcore fans.
As I always say, X6 is to the X-series what Lost Levels is to Mario.
And by the way, X6 may be the toughest X-series game, but it is a long way from being the most sadistic Mega Man game. That title, far and away, goes to Powered Up.