It's foolish to try to predict a hit.
I cannot imagine a world in which Rogue Legacy is not a hit.
There's no question that Rogue Legacy owes a massive amount to Spelunky. But crucially, it's an evolution of the type of game, not a mimic, a festival of completely original ideas on top of a familiar roguelike platformer mechanic. In each new game a castle (and later tower, forest and dungeon) is procedurally generated in gorgeous 2D pixel art, into which your brave hero must venture, gathering gold, blueprints and bonus items, seeing how far he or she can reach before inevitable death. But rather than starting again from scratch, here every death is met with progress.
Firstly, the next character you play is one of three descendants of the last, each with a collection of unique traits. You might have a Lady Barbarian, a tank character, with dwarfism, and a spell ability that sends scythes flying out of her. Or perhaps a Knave, low stats but with bit critical hits, born with hypergonadism meaning he's "perma-roided", along with gigantism, and an axe spell. The again you might get a Mage, weak but with stronger spells, who happens to be gay, and also hyperactive. Some are colour-blind (game in black and white - and yes, they already know that's not colour-blind), others are short-sighted (the screen gets blurrier the farther away it is from your character). Or how about an Assassin with hypogonadism and IBS? He farts as he jumps, and possesses weak limbs. Yeah - maybe not him.
Picking from three, it generally allows you to avoid classes that don't suit how you play, but still forces you into variation. I much prefer playing as the Barbarian, but they're not always on offer. Which leads me toward a class I may have previously avoided, and a new approach.
But there's far more to it than that. Gold gathered on a run can then be spent in two different ways. In the preview code I've been playing I've only access to the Castle portion of the game, and for this I have a very involved screen that lets me unlock more and more of the building (the castle growing new wings and turrets as I pick them). I can invest gold in improving basic stats like HP and magic, or improving strength to wear heavier armour. But this page also lets you unlock new character classes, and indeed add improvements to those you already have. Your Mages can become Archmages, Knaves become Assassins, Shinobis into a Hokage. Eventually you can tweak elements like your attack speed, your crit chances, your gold haul, and so on.
But then there's the stores too. Before you re-enter the castle, also unlocked through the previous page, is a Blacksmith, and Enchantress, and an Architect. The first lets you improve your armour and weapons, the second adds new abilities, and the third lets you replay the same castle you were previously in for a small fee.
To get new stuff to buy from the Blacksmith and Enchantress, you have to have found the plans for them in a previous run. Once there, you have a whole bunch of options to pick from. And the most interesting of these come from the latter: from her you can add double, triple, even quadruple jumps. You can implement dashes, letting you dart left or right (which proves enormously useful when solving some of the game's challenge rooms). And you can even add the ability to temporarily fly.
So it is that the more you play, the more involved the game becomes. The first few times I stepped inside the castle I barely lasted a couple of rooms. I was convinced that the game might be too hard, and that I was going to bounce off it. But the immediacy of another turn, and the chances offered by a new character with different skills, meant I couldn't resist trying again. And the more gold I brought back, thus the more I added on to my choices and abilities, the farther I could get. It never becomes easy - not by a long shot - but I became more equipped to cope with its busy, challenging levels. Eventually I reached a point where entering the room with the castle's boss didn't mean death in under a second!
Eventually I defeated the boss.
And in doing so, I technically finished this extended demo version of the game. But I did not stop playing. I have not stopped playing.
That's why I'm so confident about Rogue Legacy. Even when I'd exhausted it of its twists and surprises, unlocked so many of its classes (of which there are more to be added, I'm told), and advanced things such that I can get a good long way through the castle on most runs, I keep playing.
The castle's enemies are varied in their attacks, and many are devious. That keeps things interesting. The occasional encounters of giant versions of regular enemies are daunting, and still mostly finish me. The new skills I'm still adding still change how I approach things - I'm really not sure how I feel about flying, still trying to figure that one out. Still, still, still. The game just keeps offering more, and this is with only a quarter of it available to me.
It deserves a success as big as Spelunky's. It merits it. That it can provide the same insanely moreish desire to play again and again and again, but at the same time sustain a sense of continuous progress, is a massive achievement long before the game's even finished. And here's the thing: say it could be completed after a squillion plays through? Start again! It's a roguelike after all - it'd be a new experience all over again.
I was wrong about something once (I thought I'd got something wrong, but it turned out I was right) so I accept it could happen again. But I feel it's safe to say that if Rogue Legacy isn't a huge success, then there is no justice left in the universe. I've played less than a quarter of what the game will eventually offer, bleeding it dry of its treats and secrets, and yet I keep playing. It has the compulsivity, it has twenty buckets of unlockables, and perhaps most importantly, the platform game inside it all is great fun to play. This should be big.
You can pre-order the game as of now, for $10. That will include the soundtrack, which is especially good.