[phil_]

Have you tried Super Metroid? Should be a given, might not be, I dunno. But you really should play it. Or Metroid Zero Mission, that's good. Aria of Sorrow is my favorite Castlevania, but it's probably not the best anything and I just got excited by the giant skeleton monsters. I do love me some goryo.

Now, if you want a 2D Metroidvania that isn't Metroid or certain Castlevanias, there's always Cave Story in its many forms. Or Drill Dozer, though that's less applicable since the levels are discrete and most of the back-tracking is for treasure, but I like it so much I gotta recommend it.

As for borrowing, heck if I know. I can't make anything without stealing ideas; you could at least credit major influences, I guess. Just don't do the exact same thing the original did with every idea you borrow and I'm cool with what usually comes out, but I'm not a very critical audience.