Any links to his project page? I suppose I can just google. Another thing I have noticed about some of the metroidvania games is that while they are very big they aren't "IMMENSE." Take a look at Castlevania 2 where you could enter a church, shops, or building by pushing the up direction while in front of the door way. If this was implemented in the same manner in the metroidvania games you'd be taken to another level of castle depth. Not only could you go up, down, left, right, to various stages but the castle would essentially have "depth" layering. A game you might want to take a look at that played with this a bit is the old Barbarian II (Axe of Rage Game). Many many times I got lost even with a map (albeit, it was an overhead map in a booklet and not an automapping system).
You put something like that in a game and you can move to secret rooms, parallel zones (think Deadly Towers for nes but without the 3/4 view & movement). Now for a set of RPG games that used a similar like engine check out Heroes of the Lance and its sequel Dragons of Flame (I think that's the sequels name). It used AD&D stats and consisted of a party of adventurers that you could switch at a moments notice. That game had a crummy game interface IMHO though.