I beat Dark Souls a few days ago but I have never played Demon's Souls. Would it be worth my time to go play Demon's Souls now that I've completed its successor?

Yep. They're pretty much the same game to be honest. Demon Souls is just a little bit less refined in some of the over-arching concepts.

YES. You should if you liked Dark Souls. I still plan to go back and replay Demon's Souls after I've finished this. Even though Dark Souls refined a lot of the ideas, it doesn't replace it's predecessor in my mind. Both are great.

Maybe because it was the first, I do feel Demon's Souls was more iconic. I might actually say I like it more. Dark Souls is a much bigger game, but it does recycle a lot of the same ideas, truth be told.

World 1 is like Undead Burg & Parish. World 2 (or parts of it) feels like Demon Ruins, World 5 is basically Blighttown (but even harder to navigate). Even the Asylum sort of reminds me of World 4. Same with the enemies. Demon's Souls has its own giant flame spider, big ass armored golem, bridge dragon, HUGE monster coming out of lava, etc.

But all in all, they're different enough to feel like a unique experience.

@agemyth: Yes.

Absolutely.
 
Managing your moon grasses and burden weight can still be a hassle but it's an incredible game and you'll probably like it as much as you liked Dark Souls.

If you enjoyed Dark Souls, then yeah, sure. It's almost the same game.

yes go for it

Sorry to ask here, but, the story is any related?