As I stumbled passed the last words in Quentin's chapter, not much clarity came to mind. From the beginning of Quentin's chapter I was expecting it to be much easier to interpret than that of Benjy's, but boy was I wrong! Quentin's rambling sentences and confusing punctuation lead me down a spiraling tunnel of wonder. Though Quentin's chapter did in fact present a much better interpretation of the events going around him, than Benjy's, his use of poetic detail was confusing. This is seen in Quentin's chapter on page 74 when Faulkner writes; "when you leave a leaf in water a long time after awhile the tissue will be gone and the delicate fibers waving slow as the motion of sleep. They don't touch one another, no matter how knotted up they once were, no matter how close they lay once to the bones." Though Quentin's story depicts the scene elaborately, it is hard to understand the entirety of the language.
Now lets answer some specific questions;
Does Quentin maintain a clear sense of the "I"?
Personally, considering how Quentin's chapter is mostly focused on the emphasis of detail and essentially incorporating various clues I would say no he doesn't. It is hard to tell exactly who the speaker is in various passages and who each paragraph is referring to.
What does Quentin's narration suggest about his mental state?
Quentin's narration suggests that the oldest Compton is not in the best metal state considering his consuming thoughts throughout his story. For example, his love for Caddy seems to put stress on him as the story progresses.
Essentially, the questionable jumbled sentences and poetic writing tripped me up the most in my reading.