Fact: no one sounds that much like Opeth except a few worthless clone attempts that aren't interesting. Anyone who tries to dispute this is wrong.
That being said, if you want things sorta similar to Opeth that don't suck, you don't look at progressive death (because that's not really what Opeth is since progressive death is Death/Atheist kinda stuff), but usually death/doom with clean parts mixed in (your best bet is Novembers Doom), or just generally sorta progressive metal bands with similar emphasis on the clean/growl/light/heavy contrast (Enslaved and Agalloch are the most popular ones with Opeth fans) or a few random ones (Katatonia's Brave Murder Day, Edge of Sanity's Crimson)
So if I had to suggest some things I would go get:
Dan Swano - Moontower (If you aren't into as much extreme metal, you'll still probably like this a lot)
Novembers Doom - The Novella Reservoir (I have the last 3 and they're all decent but this is the only one I listen to much, I've been meaning to check out To Welcome the Fade when I'm in the mood)
Enslaved - Ruun, Vertebrae, Below the Lights
Agalloch - Pale Folklore, Ashes Against the Grain, The Mantle (The Mantle is most often regarded as their best but Ashes Against the Grain is probably better in a metal context)
Katatonia - Brave Murder Day
Edge of Sanity - Crimson
Gwynbleidd - Nostalgia (This band was heavily influenced by Opeth and their clean parts are pretty good but their metal isn't really that special)
Also I sometimes connect Diabolical Masquerade to Opeth for the heavy/clean contrast and a few similar guitar styles, but so many people still relate them to black metal for some reason so w/e (I really don't see it besides in the vocals). I'd check out Nightwork from them, if I'm remembering correctly that was the one where I noticed the most melodies and contrast, thought Death's Design is good for something different I guess.
Try Cynic too, they aren't similar but a lot of Opeth fans love them.
Edit: It should be noted that Opeth was my first band with distorted vocals and I initially hated extreme metal, and this is, with a few exceptions that I just happened to discover more recently, how I started off getting into more extreme music. So this list essentially proved successful for me and now I'm into more death/black metal so ya if you want to just appreciate metal more....yea...