About Me:
My non-MF gear on Live puts me at about 64k damage, 42k hp, and about 400 all resist. I beat the game on Inferno in patch 1.0.3 (the night before 1.0.4).
 
1) As many have already said, the health scaling is not proportional with incoming damage increases.
 
In Inferno (10), the mechanics of the game are unchanged (duh). This means that it will simply take a lot longer for you to kill things, though they do hit significantly harder. As a DH, this doesn't really bother me as I was accustomed to either avoiding taking hits or tanking them with SS/ShP. As for the health, it is significant. Depending on the type of elite pack, the rare mob had anywhere from 54 to 128 million hp. In act 1, the larger "tank" mobs had 100mil+ hp, just to give you an idea.
 
The biggest impact for Demon Hunters will be for those heros who lack the Legacy Nat set, wherein your discipline does not last forever. I'll talk about what I consider to be a buff to Shadow Power a little later, but just note: The better you are at managing your hatred/disc resources, the easier time you'll have in higher MP levels (no brainer).
 
My Thoughts:
I would like to see the damage scale higher in the later MP levels, such that it really is more  punishing to play at higher levels, not just take longer. A real benefit here would be something to strive for beyond just "more damage, so I can kill things faster".
 
2) With MP1, I no longer see a difference in ilevel of rare/magical drops between Act 1 and 3.
 
Out of a full hero inventory of rares (I picked up all) in Act 1, with MP=1, the vast majority were ilevel 60+. To be clear, there was one ilevel 59 rare. I didn't pick up the blue drops, but I glanced at them as they fell and found it to be a similar case - the ilevel is  significantly higher than previous 1.0.4 A1.
 
I would say it is similar or better than pre-1.0.5 A3. The change to remove ilevel < 58 drops is especially noticable, and the result is flat-out better drops across the board now in Inferno.
 
My Thoughts:
This is solid, and exactly what people asked for. We can now farm any act with similar efficiency, which really opens up the game (I always loved A1).
 
3) At the mid-range of Monster Power levels, I was surprised to actually enjoy the increased "difficulty".
 
At around MP6 Inferno, which was quite doable in my current gear, mobs took long enough to kill that I wasn't facerolling, and yet not so long that I became bored or frustrated. Personally, finding enjoyment ingame with one-hit kills vs extended battles really depends on my mood - the exciting thing about this patch is that I now have the opportunity to specify. Not only that, but when I decide to opt for a more drawn-out fight, I receive better rewards!
 
My Thoughts:
Aside from the aforementioned "too much hp at mp10, not enough damage" issue, I LOVE that I can now set my own pace. It's really fun, and a great addition to the game (and dare I say, very similar to D2).
 
4) Faster identify is surprisingly satisfying.
 
Thank you for this Blizzard - I didn't realize how much I wanted it until you gave it to me. It's painful for me to ID items on live now.
 
5) The implementation of diminishing returns on CC is subtle, and enjoyable.
 
CC hasn't been necessary for me to clear trash for quite some time - that said, it is very satisfying to at last see it have an impact in Inferno. The gradual reduction of duration is subtle and feels pretty good, "Ha! gotcha... hmmm, you seem be adapting, not unlike the Borg!!!"
 
6) Demon Hunters really needed some work/help, and they got it.
Disclaimer - this more DH specific stuff, mostly for other DH players. I'll break this down by skill:
 
Sentry: I was very excited about improvements to this skill, and sadly am still disappointed with it in the PTR.  
 

• The change from discipline to hatred is perfect for it, and much needed.
• Both the cooldown and duration are too long, for it to be a viable tool on my bar. With the cooldown reduction rune, you can put one of these down every 6 seconds. This means it takes 12 seconds to get 3 down (assume it starts off CD). This is too long. While at higher MP levels you MIGHT stay in a room that long (definitely for elites), it just doesn't fit the rest of the DH kit very well to sit in a room and lay traps for a quarter of a minute. This problem is worse when you're dropping on-the-move (as most DH are), where it takes a full 18 seconds to renew 3 of them. As it stands, the CDR rune is necessary to even contemplate using it, so I'd recommend dropping the non-rune cooldown to something like 5 seconds, maybe 3 with rune? It needs tweaking.
• At 30 hatred, we don't need it to last 30 seconds (60 w/ passive). It just isn't necessary. I'd rather be able to redeploy both quickly as I move to a new room, and redeploy them again as they dissipate. They need to feel light, powerful, and fun to use. Long cooldowns don't get us there (see: Rain of Fire).

Perfection (passive): This passive is now a must-have for anyone who hasn't hit the optimal gear-level yet. I really appreciate that you've added some options for people to get some broad stats from a skill, like the other classes, meaning the gear requirements aren't QUITE as high. This also goes a long way towards Demon Hunter tanking, which is an undeniably fun niche archetype.
 
Companion: The boar is now a standard component of my skillset, hands down. At Inferno MP6, it was able to stand in the middle of a large crowd of two elite packs, its health not even wavering. While it does not "taunt", it definitely disperses the aggro of large groups of trash or elites, meaning you don't have to kite quite as many. It feels really great to have a pet, given the class style, so thanks for that Blizz!

• The buff to resist was much needed, and really puts this guy on the map. (with this and perfection my all resist goes from about 350 to 475)
• The wolf rune still doesn't do enough damage to make it worthwhile. Don't get me wrong - it's better than it used to be, and at least it doesn't die instantly, but it's not enough.

Shadow Power (gloom):  It feels great. For those of us mid-range demon hunters, without legacy nat, the duration increase will greatly outweigh the damage reduction nerf. I love that I can press this, and not feel like I have to dump all my hatred at EXACTLY the right moment to get the most out of the lifesteal.

• The lifesteal % is still plenty.
• The duration is awesome, much more flexible.
• The damage reduction nerf doesn't stop it from saving you. (including reflect damage)

Vault: This change hasn't received a lot attention, but it is significant for me. For a long time now I've felt that I needed SS, ShP, AND Vault on my bar - one grants safety from CC, another longer-fight protection, and lastly mobility. I can now get mobility and CC safety from one ability!
 
Bola Shot: Awesomesauce. One of my favorite leveling runes was thunderbola, and the increase in damage radius is a quality of life change that was much needed and much appreciated. With the 20yd radius rune, I actually feel like I could use this as my main AOE spell.

• Something needs to be done about "disappearing bolas". My own preference would be that bolas which are attached to a dead mob, explode at the locale of the corpse, wherever that may be. It is frustrating and doesn't make sense that they just "disappear".  

6) Conclusion:
 
I love it. There are definitely some tweaks that I would make, but the overall direction of this game is only upward - I just hope some of the people who have left will take note and give it another shot.
 
I definitely still have concerns for "end-game content", but I realize that expectations run very high in this regard, especially considering this is a no-subscription game. I have not yet tried the Infernal Machine, but it looks like an amusing time filler.
 
ps I found a Legendary (ilvl 60) in the first 15 minutes of play. That RNG...

 
http://img15.hostingpics.net/pics/468637dasd.png
 
Je l'ai laissée par terre de rage.  

Meteor
   
    Delay between cast and impact reduced from 2 seconds to 1.25 seconds
    Arcane Power cost reduced from 60 to 50
    Skill Rune - Star Pact
     Proc coefficient reduced from 0.1 to 0.05
    Skill Rune - Meteor Shower
     Proc coefficient reduced from 0.25 to 0.10625
    Skill Rune - Liquefy
     Proc coefficient reduced from 0.125 to 0.10625