Some thoughts from a hardcore Souls player (beat both previous games twicemore into helping people beat bosses than PVP).
Atmosphere is classic Souls. If you want more story, go play Assassin's Creed.
Ability to customize your character's appearance more is awesome. My gf is a graphic designer, spent 2 hours working on my dude, and now he looks like a pissed off Jamie Lannister.
Definite Dragon's Dogma influence on the look of armor. Capes look cool.
The game is not as hard as previous games. Here's why: Estus plus Life Gems, improved online stability makes summoning easier, I feel like I'm leveling up way faster, and the game is just less devious than before. Example: I saw a preview where you had to fight this dude throwing axes as you walked up a narrow plank. In the actual game they toned that down. It just feels more like a fair challenge rather than Super Mario 3 ridiculous challenge, which I guess I miss (but I'm not that far yet).
Still with any complaints I'm having more fun than any game since the last Souls game. Playing online with other Souls heads is still sublime.
Well, obviously bosses will seem easy if you summon two phantoms for each one. The ones in particular that seem easier are the humanoid types, maybe I'm just better at fighting them. At any rate I've run into several that were much harder than any of demon's souls bosses and tougher than most dark souls bosses. And I'm not far in.
Summoning definitely does help a lot and it's extremely easy compared to dark souls, where I never even bothered. Especially on the PC version. One of the big things is that you can easily turn human anytime, so you can get to a boss then unhollow and summon. Personally I just do some practice runs as a phantom and then go in for real, so far I haven't failed yet using this strategy.
Life gems or not healing is far more limited than the first two games. They aren't that common, and estus shards are rare...I think I only have 6 estus and I've been playing around 14 hours. I don't know how you can say healing is easier to come by than demon's souls where you'd have functionally infinite full healing grass after one run of 1-3.
As for that example with the axe guy in the trailers - I've definitely run into some serious bullshit moments which make that look like nothing. Two in particular. But the rewards for beating them were great, so I can't be too mad at it.
ALSO POISON SUCKS JESUS CHRIST