It is a truth universally acknowledged that extremely difficult games can be the most rewarding-- provided, of course, that the challenge is fair and arises from game design and not shoddy mechanics or programming. The greater the struggle, the sweeter the sense of accomplishment, et cetera: all common knowledge, old-hat, game design 101.
Seq.Breaker has a high difficulty level, but it's not intended to directly function in this same way. Rather, the difficulty is intended to be almost a kind of deterrent to taking a heads-on approach, a way to motivate the sort of outside-the-box player thinking upon which the game turns. If an area is much too hard, chances are there's a way to skip it; if a boss is giving you grief, there's some sneaky clever oh-my-god-I-can't-believe-I-didn't-think-of-it-before way to take him out of the picture. By making the game insanely difficult, I hope to get the player to work smarter and not harder.
And, if the player wants to man-up and do it the "correct", not-quite-impossible, non-sequence-breaking way, more power to 'em. There'll be that conventional sense of reward waiting for them on the other side. But if they break the sequence, I think they'll find an even greater sense of reward-- "I'm smarter than that lava boss, so there."
And either way, you'll always unlock the next mission; there's no penalty for playing the game you want to play it. That's important to me, and I need to keep that in mind as I continue working on the game.