When people say this game is hard, I think they mean they're fighting with the camera, because the enemies are easy.
Well, they are kinda right about the combat system. It is really nicely designed, and for the most part, is one of the best, it not the best melee combat available outside of the fighting game genre. Granted, I think it could use a lot of improvements (I'll list some improvements later), but really is nice. Especially when fighting the red (or is it black?) phantoms, the duels are memorable and highly enjoyable. The problem is they don't respawn...
I see this game as Diablo/Borderlands that made combat fun... but it gets old. Here comes the main focus, the bad stuff. If you didn't experience any of the below, I wonder if we really were playing the same game. I also expect a lot of the fan boys to dismiss this without even reading this anyway. Whatever, nothing new.
For one, the majority of the enemies you face get boring and easy to fight against as they have a few set attack patterns and are highly exploitable. At a certain point you'll just learn exactly when to parry or dodge>backstab and combat becomes really easy. If you can't get the timing down, you can often exploit the A.I. or just "farm" the early levels, and build up the stats and upgrade the weapons you need, and then go back to the later levels. But this can get so tedious, and having recently taken up painting I can say with certainty that watching paint dry is more enjoyable (because you're at least doing something productive). And unlike the aforementioned Diablo/Borderlands, at least you are capable of getting worthwhile loot. In Demon Souls, even with a high luck trait, the kind of loot you get is just pathetic.
Once you have 99 of each kind of grass (both on hand, and in the storage) off to the other areas, which happen to suffer from terrible level design. Not to say the first mission is great, like the awful lighting (where the 5 boulders roll), but at least the large areas allow for you to play various styles (kinda). But the Mine level (for example, the others are pretty bad as well), bring in one of the biggest issues this game has: camera angles and the camera lock.
Back when I first started this game, the tutorial area, I noticed something that would foreshadow a lot to come later. When facing the second zombie, and you lock onto him with R3, your.view is obscured by a beam. From that point on, it happens quite a bit in the beginning, but becomes more frequent, particularly in the aforementioned mine level, in the prison(?), and the canyon filled with those plague guys. If you try to use the R3 lock-on, and it actually works (more on this later) more often than not, your view will be obscured making it hard to react. You lose some health, no biggy, sometimes you die (from the "stronger" enemies) but it happens a lot more often as you push onward, and without a save feature, checkpoint or short cuts (like at the castle) it really gets tedious to die from camera issues. Eventually, when you don't die initially, you lose a lot of those grasses and need to go "farming" again because their frequency in those other levels are next to no where.
Now, R3... when it actually locks on, and your view isn't obscured, it is a great feature. But the problem is it doesn't always lock on. The enemy can be in clear view, and the camera won't lock on. Sometimes the enemy can be partly obscured (or completely) and it will lock on, but mostly it won't. Or if you're facing a large group of enemies, sometimes it will lock onto the nearest (which is good), sometimes it will lock onto a slightly further enemy (which is bad). There are countless times where this has happened; I come across a group of enemies and I don't feel like cheesing out and taking advantage of the terrible A.I. so I jump into the fray and use the skills I've honed from playing the game for many hours. I try to lock onto the nearest opponent, but it locks onto another one, and one you lock onto them the left analog stick, and the movements you make with it, move in relation to the enemy you're focusing on. If you're locked onto a further enemy (who might happen to be at a different angle from the nearest), you movements can often get you trapped in a corner or strafe directly into the enemy you wanted to focus on. Sometimes moving the right analog stick remedies this, but sometimes for some stupid reason, the one opponent you want to lock onto cannot be focused onto. This little issue, which happens A LOT, often can result in you dying, and because of the lack of saves/checkpoint system, you need to start all over (and if it happens again, it often does, you'll lose all those souls you've accumulated). Now, when people say this game is hard, I think they mean they're fighting with the camera, because the enemies are actually easy.
The boss battles, when you have room for the camera, aren't hard, but certain areas (like 2-2), it is problematic and results in your death. Now, yeah, you could "just learn the layout" of the arena, but getting there is tedious, fighting stupid bug creatures, in tight caverns (which limits your approach... oh look, and "RPG" on rails) and no short cuts. Do I really have to kill several massive bugs in tight quarters running left and right a few feet, hit once, dodge, hit again, and do this for a long time because they have so much health. It's not fun. It's easy, yes, but it gets boring. You die at the end because of a bad camera, do it all over again. Terrible design and insulting. Also, on many occasions, the frame rate gets so bad the game becomes a picture book in.
Speaking of bad design (and stupid ideas), this game is full of it. Here are some examples: tutorial boss. Run to one of his directions, hit him a bunch of times, and then dodge hit butt attack. Continue for a few minutes. SNORE. Rolling skeletons... what? Initially it's hard, but a well timed halberd (which is too good) strike kills them before they can do anything to you. But still, no stamina rules, no nothing. Even if there is a distant barrier between you and them, they'll just keep rolling, and I'll be hating (it just looks so stupid). Why not give them the A.I. and abilities of the red/black phantoms. The rag dolls/physics are also really bad. Am I supposed to believe that an opponent that was able to do that much damage, be so light that interacting with their corpse makes them fly everywhere?
Also, the voice acting and story are... uh, not that great. Save humanity from extinction? Snore. That's pretty much every game ever. And the lines and how they're delivered, "so the world will be mended," did they (From Software) intentionally look for a voice actress with a speech impediment or they just intentionally pick the worst take from the recording session? The story is so skeletal it practically isn't existent and there is no reason to care for any of the characters much-less your main object (kill demons or something?).
Lastly, because I've already spent enough time writing this and playing this boring game, the label "RPG" on this game can never be so wrong. Just like the previously mentioned Diablo and Borderlands series, this is not an RPG. It has RPG-elements, but it is an Action Game. If it were to be called a RPG, it wouldn't be so linear (I mean if I were to pick the Thief character I'd like to be able to steal something or at least have access to more back stabs, another issue, but in a tunnel, where can you do that?). There would be a story. The characters would be interesting. Maybe there would be dialogue options (aside from "accept the quest"). No, Demon Souls is not an RPG, it is an Action Game with few good ideas ruined by the lackluster execution.
Things that could of made this game as great as countless people say it is:
Better combat. Include more directionals for varied attacks and have more that just two stances. Yes, I just changed stances with a sword, yet I'm still doing huge arching attacks that collide with the walls (hit detection is also bad in this game, like getting hit through walls in those tunnel levels). Replace all set movelists of the opponent and give them a functional A.I. Give more animations to back stabs and parry>counter attacks or give them different properties. For example, doing a back stab, and the animation of kicking the body should do damage to surrounding enemies. It would be a nice touch.
Actual RPG elements. RPGs are about choices and having a variety of paths available. If all you have is a tunnel to go through as a Thief (Assassin is more suiting in my opinion), that's JRPG style (i.e. stupid game on rails).
Either better level design or a better camera. Or a save function/checkpoint system to compensate.
You now have a really good game. But where it actually stands, this game is kinda bad.
Because I got into this game so late, I haven't seen anyone online at my skill level so I cannot comment on the multiplayer aspects.
Lastly, I think this game was seen as a "breath of fresh air" by many because the current state of gaming is that games these days are designed to hold your hand (recharging health-bars anyone?), and while I do like the concept of a game like this, there are too many flaws that just this game a waste of time. And this is coming from someone who really enjoyed this game at first and still want's to finish it due to a OCD-style mindset. It just isn't worth it. There are hours better spent making real money at work, playing better games, studying for school, learning an instrument, learning a craft, yada yada. Enough time and words have spent writing this as well.