Hmmm barriers to playing before hand. Ill try to remember but I didn't have as much problem as most other people because I HUGGED the Wiki.
Mind you that this is observations I made at the time and not currently. I also don't offer solutions.
Adventure Mode:
-The problem with adventure mode is that overall it is pretty much unfinished. So my comments on it arn't all warrented.
1) Adventure mode was nearly impossible: I always picked "Start Now" and didn't know it started me off naked without weapons and next to powerful enemies. So I always died. I even used random objects laying around as weapons thinking it would improve my chances. In fact I didn't even know I could wrestle until much later.
2) Equip screen in adventure mode is a fruitless exercise even now: I don't even pretend to know how to navigate the equipment screen in adventure mode...
3) Caves are mindless and random: There seems to be little rhyme or reason to caves. You could search forever and never find the boss while fighting random enemies laying around
4) Dark Fortresses are impossible: Dark Fortresses seemed impossible, Enraged goblins destroyed my early adventurers. (I actually never fought their archers) While I enjoyed fighting them it was more because there was nothing else to do.
5) No mid difficulty: It seems that everything either is easy to deal with or nearly impossible. So I could do the easy Caves or impossible Fortresses
6) Caves are sometimes impossible to find!: Yes I can't believe I forgot about this. My greatest peave is that sometimes it was nearly impossible to even find the cave your looking for.
7) How do I make money?: I tried desperately to get money so I can get better equipment. Unfortunately I found that missions gave nothing and Goblins didn't give me usable equipment (I am also a goody goody so I didn't kill my own people). Though it wouldn't matter even if I did find sources of money because:
Trade screen of missery: Trade is hopeless. How am I supposed to buy anything if he won't show me a price of give me an indication of what he wants? Even today I don't even bother.
9) Towns of Missery: Where am I going? What is this building here? I think I will go in it and go to the top! Ohh my goodness how do I get down? This is going to take forever! I just want to find the castle so I can speak to the king is that so much to ask? Ohh wait now I am at the castle... Now where is the king? He isn't at this throne? Is there a suicide button anywhere?
Fortress Mode
-Overall I had less problems with Fortress mode because I hugged the Wiki.
1) Information overload: There are so many things on the list but I have no idea what is essential. I pretty much had to use the Wiki.
2) I was supposed to be prepared already?: I was attacked by a Trog or Kobold ambushes rather early
3) *SNORE* Defense: Because I could never get my military up before I was attacked and killed I did perfect defenses. Which made the game rather boring. Goblins never became a challenge at any point of the game.
4) Mechanical devices...: Even today I don't bother with the mechanical devices (specifically things that give and produce power) they make little sense and the Wiki isn't as helpful as it could have been.
5) Barrels, Bags, ohh my!: I thought I had enough, I guess I should build even more!
6) What am I supposed to be doing?: I was aimless and building things not knowing what it is for. What is a Quern and why do I need it? How do I even advance?
7) Trade Depot of horror!: Ohh my I just remembered how much of a horror it was using the Trade Depot. I ain't going to lie, it took me a few months to even bother with it and a few more to put it down correctly. In fact a lot of my frustration with the game (and probably explaining my lack of military)
Mountains are for sissies!: I actually liked Non-mountains more then Mountains. Thus I often had to deal with aquifiers and lack of minerals even if I did manage (Though differing biomes) to get past them. So I had a unknowingly tougher time.
9) Fuel what is fuel? How do I get coal? Why can't I use Wood?: The fact that you need to burn wood to get fuel is against your instincts. I certainly didn't think that is how it worked and I ended up thinking that Fuel was some sort of endgame item.
Both:
1) Goblin, No Goat, No wait it is a Giant!: Ohh my goodness the second I got a Graphic pack I never went back. I was going out of my mind not knowing what I was fighting unless I specifically looked (and when your wondering if that is a Dog or a Dragon... sometimes the excitement makes you run without looking).
-Id personally would think this would turn most people off. Because not only do they have to learn ASCII but even if they did they could be murdered by mistaken identity.
This is overall all I can remember but even then I don't think my list is accurate or complete. I also doubt I am typical.
Ill think of more later.