I actually bought Demon's Souls when it first came out on PS3, it was exclusive and it was right up my alley (since I love hard games, gothic atmospheres and medieval fantasy)....but I literally played only 1 hour of it and put it away never to be touched again for ~7 years.
It was a combination of things, at the time I pretty much had stopped playing VGs altogether because of the girlfriend I had at the time and some motivation to put my time into more productive and lucrative endeavors. Also it didn't help that the first hour of Demon's Souls had 3 extremely unfair and cheap OHKOs that I was not a fan of *controllers hits wall*.
Anyways long story long, I finally have fully played and beaten it recently. Actually got addicted to it and binged it, getting platinum in just 2 weeks. It's a great game but man it has some serious flaws, both from a design aspect and controls aspect. People still seem to be quite brainwashed about the game, maybe they were just so used to playing crappy games that they think the souls series is perfection (blind to it's flaws). The game has a terrible lock on system that can cause you to easily suicide, there are traps that are insta-kill and they are un-reactable, the world tendency system and upgrading system is really broken and unbalanced, the environments are poorly programmed to the point where you never feels as if you are in full control of your character.
There are 2 bosses that are spectacular, like Shadow of the Colossus spectacular. The rest are way too easy, the mobs and general enemies are the most fun and figuring out their AI and attack patterns reminds me of Mega Man or Castlevania. Magic and Bows are way OP and uninteresting, unfair enemy stats (infinite stamina and MP), everyone's immune to poison and bleeding effects (so what's the point?), pathing and obstruction of enemies and the environment is always a problem that detracts from the gameplay.
I'd still recommend it to anyone with patience and love for this time period of fantasy action. The ideal way to play it is to have 2 save files; have one be the dummy test character that plays through a level first and dies 20 times to BS and unknown enemies, then have a second that is the real character that you can try and make it through without dying, parrying and backstabbing everyone like a boss, and now you know about unfair BS and traps/hazards.