Yeah, the castle layout can be confusing at first, but Dracula's castle is supposed to be a labyrinth after all. Here's some tips that I hope will make the game more fun for you. First, keep checking your map until you get the hang of the castle layout, and then keep checking it even after you do. Explore each and every room to find everything, you never know what that one tiny room might contain. Most of all, use the dash buttons for movement instead of the dpad, as it makes exploring the castle significantly faster, and a lot more fun.
I don't know what to say about your disdain with having to equip items to continue, as that is a mechanic Iga used throughout the series, although I suppose it is a bit more prevalent here. For example, Aria of Sorrow requires you equip certain souls to get past the waterfall, and also requires a certain set of souls to access the Chaotic Realm. In Dawn of Sorrow you had to equip Mina's Talisman to unlock the last few areas. That's just a couple examples I can think of off the top of my head. I can see how having to stop to go into a menu to equip these items can disrupt the games flow, but look on the bright side; now that you know about the controller shortcuts you don't have to go into the menus to change your spell books anymore
![Smiley :)](http://www.nintendoworldreport.com/forums/Smileys/default/smiley.gif)
As for the locked doors, here are some spoilers if you want to be a dirty cheater: the rainbow doors are opened with the Lure Key, which can be located in Castle Entrance B. The skull doors are opened with the Skull Key, which can be found in the Luminous Cavern A. You'll also need to equip the Crushing Stone to be able to destroy the stone walls.
Good luck in your quest to slay Dracula, and I hope you start enjoying yourself more soon.