You could always download the PC version for free and try that.
http://spelunkyworld.com/original.html
Not sure how different it is, I just learned of the free version myself and have literally just downloaded it upon reading this thread.
Aside from the obvious HD-ification, the old version has fewer monsters and items, no multiplayer modes, and lacks the ability to pick which damsel (lady, man, pug) you want to save or which character sprite you want to use. Other than that, they play more or less the same - if you really want to gauge whether this is worth your money, the original is definitely a good barometer.
Really, it's a fantastic game for people who like losing - and I mean that sincerely. It's sort of a 2D platformer roguelike; what Binding of Isaac was to top-down shooters this is to Castlevania. It's the sort of game where you're carrying a damsel and toss her down into a pit only to trigger a turret you didn't see that shoots her across the map into an idol that triggers a boulder to run you over, and the result is hilarious even though you have to start over. If that's the sort of thing that excites you, the game is absolutely great. If that sounds frustrating and dumb, stay away.
Tried the demo, intrigued but yeah it's definitely quite a hard and challenging game.
Sorry if this has been asked but:
1) Are there any checkpoints of any kind in this game?
2) How long is it?
I don't wanna maybe buy this and then just find myself at a brick wall unable to continue, after I'm assuming the demo was the easy stuff =/
1) You can unlock new shortcuts to each "world" after getting to it a few times. Each world is 4 levels long, and there's I think 4 worlds total? But yes, you can slowly buy shortcuts to the subsequent levels by giving the shortcut tunneler guy bombs and such. Once you've paid him enough visits and given him enough of what he needs you can skip straight there.
2) There's an achievement for the game to be beaten in 8 minutes, so if you're looking for raw length of the game this isn't for you. However, no one -
no one - will get 8 minutes of gameplay out of this. It's too hard, and there's too many interesting things to find and characters to unlock. Really, the length of the game depends upon how interested you are in playing through pseudo-randomized action platformer levels while collecting gold and avoiding monsters in wacky situations. For some people it's hours and hours and hours, for some people it's not.