My Dying Bride = great. I dont know where the best place for you to start is though... Like Gods Of The Sun, The Light At The End of The World, The Dreadful Hours. I would say any of those three is a good place to start with them, but you might want to check with Bouville.
Opeth, you already have their best album, but if you like BWP a lot, you'll like Deliverance. So I guess go with that.
Katatonia, I'm not to familiar with, but I really like Viva Emptiness.
Other good melodic death bands... Dark Tranquillity and Arch Enemy come to mind. Neither of their newer stuff is quite gothenberg anyway.
Also, they dont exactly fit into what you mentioned in this thread, but you should look into Amorphis. I love them, and if you like this stuff, you'd probably really like them too.