Basically, it's full of bugs, glitches and glaring errors such as you finish a quest, it goes to a cut scene and the cut scene winds up leading to the beginning of the quest again and you have to keep repeating until it sorts itself out and stops being crap. People aren't where they ought to be, objects which are crucial to continuing the game are missing half the time, quests don't always update when you've finished or it says it's finished but the characters relating to it don't register and you have to start all over again and casual mode is most definitely NOT casual (I've tried the next mode up and it presents exactly the same level of difficulty which can only lead me to conclude that casual mode is some sort of in-joke for the developing team). The healing system is silly in that you need a break between being battered long enough to take out a potion and swallow it down - not likely when you're surrounded, the only team member left alive and you are being assaulted from all sides. The tutorial system is shockingly bad - vague, unhelpful and on casual mode especially I'd expect more from it seeing as the mode itself is supposed to be for people who have never or rarely play games. They presume an awful lot of prior knowledge and the game feels like it was far too overambitious for BioWare to even contemplate. It feels unfinished.
One of my biggest annoyances is the whole quest system full stop - you can highlight something as your main quest so it provides the appropriate marker. Only it doesn't. It provides markers for EVERY SINGLE QUEST in that area so you merrily make your way over to what you think is the right marker only to find it's for something else entirely and you've wasted time. There are too many things locked away in areas you either cannot or have no desire to return to later in the game (case in point - Lothering. If you don't unlock everything before you leave, you won't get a chance to go back). There's a lot of back and forth for the side quests and without a high enough intimidate or persuade level you can't get the outcome you want anyway (such as the main questline in the Brecilian Forest) - some of these outcomes are achievement related and it can be a pain the backside to keep repeating them over and over again until you have got the level you need. BioWare seem to love repeating playthroughs as well - but there are about 6 in total and it's really not that interesting enough to warrant so many especially when there are not exactly many differences in how the game is played out, despite what they say. Essentially, the quests continue as normal with one or two slight differences in dialogue options - but nothing that would change the outcome of anything important.
Also with the quests, you are often left with no indication of where to go next - especially with the side quests. You are given a vague, almost cryptic few lines of text in your logbook and then you are left to it. I've lost count of the number of times I have had to go online and look up a walkthrough just to find out what the hell I'm supposed to do next. I shouldn't have to do this at the beginning of almost every side quest - a walkthrough ought to be a last resort. An example of this is when you are in Orzammer and you come across a sick dwarf. You gain a quest whereby you need to collect ingredients to restore her health but they don't tell you what they are or what you need to do. Instead, you won't find out unless you happen to select herbalism in your radial wheel - something which you may or may not be aware of especially on your first playthrough. So much is left to assumption and my point is that sure, if you are playing on a high difficulty level then of course - presume away that the player is adept at RPG's and knows what they are doing. But if someone is on casual especially, then you need to presume idiocy until proven otherwise. No one should get that frustrated on an RPG of all things.