Please don't mind my noob review for a 1st timer...
I've just got my 8GB C3 this morning about 5 hours ago. First impression - It's so small!! (Considering I was introduced to the big brother C4 2 weeks ago).
Took me 1 hour to transfer 20GB of songs into my 32GB external micro sd and only start auditioning. By the way, I'm using a TDK BA200. For sound quality, it is definitely far from C4. However, it still carries reasonable soundstage and instrument separation. I cannot fault its sound quality for this price range. At first when I thought it lacks some low frequency, but strangely, the more I listen, the more I feel that it's not lacking the low frequency (maybe it is burnt in now).
Built quality wise... it's heavy for its size. Feels slightly heavier than a samsung galaxy s2. Looks sturdy.
Navigation - It's not difficult to do it but one thing i must comment is that it has a small display screen. You will need to wait for the auto scrolling. Another thing that i want to mention is that the capacitive touch is not the most sensitive one. It might annoy some of you but I think it's still bearable.
SQ - 7.5/10 (Benchmark against C4)
Built quality - 9/10
Navigation - 8/10