Merrill is one of my favourite companions in any BioWare game.

Everything from the accent to her personal quests. People seem quick to attribute her 'fish out of water' cluelessness in regards to all thinks Kirkwall (and Shem) as well as her isolatorary nature and overal shyness/cuteness to a lack of intelligence or an otherwise simple nature. I just can't agree with that, including what we see of her in Origins there is plenty to suggest she is a bright and friendly person amongst her own people with a keen enough intelligence to warrant a wise Keeper like Marethari placing her trust in her for the future. Plus having been in the position of country bumpkin moving to the big city I can fully sympathise with some elements of her lifestyle there.
Obviously the most talked about part of her character (other than her glorious Welsh accent

) is her story involving the eluvian. While it is legitimate to either support her or challenge her belief in regards to it (I chose the latter in fact and thought it played out beautifully) I don't think her, at times, stubborn desire to go through with her plan to deal with the demon reflects negatively on her (at least, certainly not wholely negatively). Over the course of her personal quests her willpower, courage, self sacrifice, and other positive traits are all displayed as she goes about doing what she thinks is best for her Clan. It is a measure of how strongly her character comes across (to me, and others) that despite having seen deals with demons go wrong time and time again, and the fact the whole thing sounds like an incredibly bad idea, she still convinces you (or comes close to in my case) that she can pull it off.
So yeah, I love Merrill. Although I can understand why some folks might not share my opinion.