I think Simon's Quest is omitted because it doesn't take place in one huge dungeon throughout the whole game and the power ups aren't quite as Metroidish.
I've always found the castle-confined play area to be the biggest weakness of the Castletroids.
I've been dying for quality remake of Simon's Quest ever since it came out.
I completely agree. Maybe I have ADD or something, but I hate the feeling of being stuck in the same castle throughout the whole game, kinda like how movies that take place in one location throughout the whole movie generally make me feel uncomfortable as well. Strangely enough, I didn't mind this situation in Metroid.
Oh and I love the Angry Nintendo Nerd, even though a lot of games he disses are ones I like. He's a funny guy, no matter what he's talking about.
Yeah, but K, all the different levels in the Castle, don't necessarily look like a castle, so it's like a whole world in a castle! And Portrait of Ruin ventures outside the castle ALOT.....well, depending on your pov.
Yeah, but PD, one of the things that I'd like is some towns/villages with different shops and maybe a decent number of characters to interact with. 
I am aware that PoR does some different stuff, but isn't also more of a level based game this time too(I haven't played it)?
When you say level based, do you mean, stage 1, stage 2, etc.? It's a Castleroid, so, you have exp. & various weapons you find or buy, & there's basically a castle, & then, you go into these portraits, which are levels seperate from eachother, of which, you can keep going into, if you missed something somewhere, but, it's still a Castleroid. You don't go thru levels from begining to end, like you would in RoB.