To me the two were almost identical. Dark Souls is the Doom 2 to Demon's Souls Doom 1.
I think the Estus flask system was an improvement as I didn't always hold hundreds of healing items as I did in Demon's Souls. I guess in some ways it made it easier to handle your resources as the bonfire always replenishes the flasks but the grass management was more like "should I throw these away because I already have about a thousand other grasses in my backpack" than anything to do with carefully considering whether to use them. With the flasks on the other hand you did often have to think about whether to use them though that may have something to do with the fact that I almost always played with just 5 flasks with me.
I can't really comment on flasks vs grass, because I never found myself in a situation where the debate became relevant. I'm always either getting killed in 1 hit on low hp builds, or float so much hp that healing with anything other than hums or blessing becomes impractical.
Hums, in my opinion, are essentially estus killers. Every mob drops hums, the streets are littered with hums, all the bosses drop hums, even stores started carrying hums after the patch, the more hums you use the higher your chance of finding hums, they boost all of your def stats, boost dmg on certain weps and act as covenant currency AFTER being used. Admittedly, the animation for using hums is slower, but the healing effect goes through at the start of the animation, so you still end up healing through backstabs, aoe dmg and whatever else.
As far as areas go I think the overall difficulty was a bit higher in Demon's Souls but some areas like the Tomb of Giants in Dark Souls was more difficult than any single area in Demon's. I also had a far easier time with the bosses in DeS but I played it to completion after DaS so that may be the reason. I do think that O & S is more difficult than any boss from Demon's though.
O&S is a trick boss, did you try soloing them? They're laughably easy when you don't have to worry about them switching targets. DeS had a lot more cramped areas, more ledges to fall to your doom, spear-chucking stingrays that aggroed from 200 m away and necromancers that spawned infinite ghosts. DaS almost seemed geared towards low level runs, as you could ignore direct combat in almost every situation. DeS, in comparison, had a lot of "corridors" with enemies stuck right in the middle of them.
Enemy variety is a bit tricky. I think the enemies in DeS were more interesting even if there were less of them. The skeletons that roll and the mind flayers felt refreshing after DaS. Also because backstabbing isn't quite as easy in DeS fighting enemies didn't start feeling repetitive so quickly. Of course I could have restricted my backstabbing in DaS but still.
I don't think self-imposed restrictions make much sense really, especially in a game that's supposed to be hard. Enemy classes are very much the same throughout both games, similar combat animations and all. DaS felt more geared towards enemies that engage strictly in h2h though; how many different types of knights did we get, like 8? They're also generally very easy to pull, and their max distance from spawn feels limited when considering the new open world design; once you find the spot where the enemy resets, you can take out any mob without it fighting back. I know it's essentially an exploit, but with the smaller, more enclosed levels of DeS this kind of pathing restriction rarely came into play (I think we had about the same pull distance in both games) which made enemies feel more threatening, as you rarely had a safe spot to stand on outside of the hub.
I think saying that DaS is streamlined from DeS is somewhat true but sounds like a bit of an exaggeration as there just aren't that many changes.
It's sort of like Fallout 1 vs Fallout 2. Both are great games in their own right, but you can tell the sequel was influenced by player feedback like "Nobody needs 'this' game feature" and "Wouldn't it be cool if?" suggestions. I also like the art style less, but that's a very personal preference -- DeS felt more like a Japanimation take on some Lynchian medieval anecdote, smiley-face squires chucking fireballs and all that. DaS had a more Diablo-esque vibe to it with all of the various demons and skeletons.
Dedicate multiplayer servers will even out the odds for PvP: less lag or both players will suffer from the same amount of lag.
The player closest to the geographical location of the dedicated server will still have a better response time, so it's still down to the match-making. Could also mean a lot of mp downtime overall.
