I ran into a nasty bug in Redcliffe where the undead would spawn endlessly due to clipping. Apparently stuck zombies trigger endless waves, making survival impossible. Needless to say, that experience was maddening.
Fortunately, after multiple, painful attempts, I was able to kill the immobile enemies quickly enough to prevent an unbeatable amount of spawns.

Damn! That's nasty.
The worst I got was when playing the game minimized, the speech options did not apear and I had to ALT-Enter it to show again. It was conistent until the end of the conversation though. Wasn't too bad. A little worrying however, since I hadn't saved in a long time.

Yeah, several members on the Bioware Social forums were complaining of that Redcliffe bug. 1.01 makes easy mode easier, allowing more users to eliminate the stuck undead more quickly/easily. Apparently, pulling the undead from the fire to the mill (kiting them to the group of NPCs) does not work because more will spawn by the fire. I recall pulling at least 7 groups of 5+ zombies that way before giving up and attempting a different approach.

Ahh, well what do I know xD
I made sure that patches were installed when I was about two hours into the game.
Edit: I had it quite easy I suppose.

I don't know, I mean, you still had to tolerate Zevran and Morrigan.

Haha! Zevran was a bastard!
Morrigan however...

Just to be curious, what kind of difficulty problems did you had ?
I play in hard difficulty and while the game is chalenging and often kick my butt it's never "ridiculouslly" hard or anything (except when I go too close to great dragons :-) ), it force you to micro-manage your team and abuse of the pause but appart from that I didn't find anything inconsistent about the difficulty yet (of course you have some "special" optional quest that feature overpowered boss but that's to be expected).
Concerning bugs, maybe I was lucky but the only I had yet (after ~60 hours) was a CTD, the soldiers peak not apparing on the map and some minor dialog inconsistencies.

I found the difficulty to be excessively variable. Some encounters, including boss fights, were too easy. Others were frustrating in their difficulty. For example, many of the scripted encounters that place the player's party in a predetermined position would not allow for proper positioning and tactics, resulting in an inevitable string of deaths. The fight against the Dwarven mafiosa comes to mind. The difficulty slider helped to resolve these issues, but I would prefer to not use it often.

I just want to know why all of the characters in the game consumed their poultices orally.

I don't recall ever seeing said consumption. How can you assume that? What secrets are you hiding?

Well I definetly agree that some "combat" triggers are very annoying, especially those that makes the enemy invulnerable until it notice you, that makes some high level spell like inferno, tempest, much harder to use (as they also tend to be "reseted" by said triggers). I also hate when you try to fire a fireball and your mage start's running toward the enemy instead.
But usually, at least in my experience, if you have enough "crowd control" spells or talents, like mind blast, ice cone, or even fireball or earthquake (or even better : a fully powered bard) you can get out of most situation with "minimal" harm.

Crowd control is indeed very powerful in Dragon Age. If you don't micro your caster(s) and properly execute crowd control, many fights are significantly more difficult.
Crushing Prison, (Mass) Paralyze, Cone of Cold, Force Field, and Petrify are amazing.

You might have to figure it out for yourself.

For some reason, in the last bit in Denerim, I had lots of very low level enemies to deal with, rather than the large groups of high level enemies that I had been dealing with previously.
Difficult to say exactly how different it was, since I only had the best version of survival (so I could see enemy levels on the map) very late on.

I don't know exactly how it's supposed to work, but IRC, the enemy level depends of you own levels when you first unlock a zone, so if you go to Denerim at one level, then go elsewhere, level up and go back to Denerim later, the enemy might be underpowered compared to you.
That's what happen to be at Redcliff castle that I unlocked at the "begining" of the game, then leaved to do other quest and only came back 6-7 level later, as a result nearly all the enemy I met there were very weak and posed little thread to my group, even in hard difficulty.