First time lurker, first time poster.
I was googling for metroidvania RPG articles/threads/whatever, as it is relevant to the interests of my small but hopefully up-and-coming studio. I'm working on what I guess you could say is a game of the Metroidvania genre. We're focusing on two aspects of the game that seem to often be lacking, while still maintaining the expansive world, the need for backtracking, and pseudo-linear progression.
1. Interesting enemies and level design. As previous posters have said, while the large, expansive worlds are nice, they are the same each time around because the combat tends to fall flat on its face. Sure some later bosses might have seemingly unavoidable abilities that put the pressure on (Ridley 2nd form from super metroid, I'm talking to you), but overall playing through the game again beyond going for all the collectibles becomes naught but nostalgia. Our game AI features a finite state machine for each enemy, allowing them to be "assisting", "idle", "aggressive", "weakened", to name a few examples of possibilities, allowing us to govern their behaviors based on these states, removing the need for cookie cutter situations. Couple this with cleverly designed rooms that promote clever decision making to take down enemies and we'll have something very interesting indeed.
2. Loot, and elements from games like borderlands. The second thing that I don't think I've ever seen done in 2D that we are shooting for is four playable classes, interesting skill trees (so that you aren't spamming your basic attack for the entire game), and the real ability to define your combat experience based on your playstyle. Want to play a character that can slow enemies, and then throw them against the wall when they get close to you? Play as a Cyro/Telekenetic Psion. Want to get in the enemy's face and do cool combos with a sword? Go for a technique Enforcer. In the end, all of the classes will have to be balanced and feel great as you are playing through the game... but it gives the player the illusion of choice and adds replay value. Couple that with diablo II style item generation and you'll be playing it over and over.
I didn't mean for this to sound like a sales pitch so please don't take it the wrong way. I'm just excited to share our ideas for how we think the metroidvania genre could be enhanced, namely by making the combat a little less button-mashy, and adding some of the RPG elements we've come to know and love in some newer games such as borderlands and fallout, without the need for flashy 3D graphics.