Hmm...this may be a little inappropriate, so feel free to delete this if you think you should, Jorge or any other mods, but...
At the risk of seeming risque, there are actually some *porn* games which are...genuinely solid Metroidvanias. The first I'm thinking of is "Nightmare Sphere." Here's the website (NSFW):
http://mickmanx.blog71.fc2.com/I don't know what the plot is, but you're this girl who gets raped by the monsters when they kill her. To keep that from happening, though, you have a very solid Metroidvania platformer mechanic with a few interesting twists of its own. The basic gist is alost exactly like that of a Metroidvania--you start out only being able to perform basic attacks and single jumps, and you start out with just a basic sword, but you can get spears, magic, and hammers, as well as ability orbs which let you double jump and dash to reach previously inaccessible areas. Much like a metroidvania game, there are save rooms, warp rooms, and a map that works in pretty much the same way as SoTN's. It's a bit more "action-y" than many CV games due to the wide variety of actions you can perform, and how bosses can get "stunned" if you hit them hard enough. Of course, if you lose to them, you get raped. :rolleyes: As a game, though it's entertaining. There are even multiple endings!
Secondly is "Unholy Sanctuary." This is another "play a female character who gets raped when she dies" game, but this time everything is based off...Ragnarok Online! The main character is a priestess and all the enemies are from that game. It's not as polished or innovative as Nightmare Sphere, but again, it's a fun game in its own right--there's no map, but backtracking, platforming, etc. is clearly based off Castlevania, and even the music is very Castlevania esc. Check it out here:
http://hatahataragnarok.blog.shinobi.jp/