Like some others have stated, the difficulty issue is not just giving enemies more HP. It is more about the game balance. For a game as big as this, with as many sidequests that ar eto be done if you choose, your reward for doing all these sidequests is a game that becomes more and more a cake-walk as you progress.
I love the game, it is one the best games I have played in a long time. Alot of great ideas, some taken from other games..but when things seem to be so good, other things appear that they did not intend to be so. For example, getting this awesome weopons that do massive damage, yet the level requirements are so low to equip these items.
The crux of the issue is that if you:
1. Do all the side quests
2. Explore everywhere in each zone
You end up breaking the game and everything is a cake walk because you have outleveled the content/enemies, you have out-geared the enemies in the zone and you end up playing in God mode.
The fix, out of many are to me not that hard to understand. For starters, leveling up should take longer and less xp should be handed out. Loot should be more in-line with the area you are in and health/regen potions need to be nerfed.
For an outsider looking in, having a understaning of how the sub-systems of enemies scalling would be a good thing to know about. I posted a dozen pages back that I decided to run from the starting area to the farthest area on the world map that I can go, which is the city with the giant console looking thing and I was able to d this with my level 5 character with the Mass Effect Armor and I did not die at all. I stopped everyonce in a while to fight enemies and did not have an issue at all.
In the end, difficulty is just one aspect of the challenge issue. Simply giving enemies more HP is not the answer because it would still be easy, just take longer. There are alot of things that would need to be adjusted and I hope they do...and not to be too negative, I pretty much have stopped playing the game because I am a completionist, I love doing every quest I find, I love finding every chest I find, I love looking for stuff revealed by the hidden detect, but doing this has caused me to be overpowered and makes the game no fun since there is no challenge in the enounters. While I statisfy my need of finding everything, doing so makes the game not challenging and for this type of game you cant punish players that do all this exploring and at the same time make the game too easy for them because they chose to do alot of exploring.