That was an enjoyable read. I liked the quick pacing, and the art packs a lot of personality and expressiveness. The three protagonists seem to have different/unique personalities and mannerism, and it should be fun seeing that get fleshed out!
I agree with the others that the foreground blends in with the background too much. It's not a matter of increasing contrast overall; it's a matter of separating the focal elements (usually the characters/foreground) from the rest of the image. One way to do it is to increase the contrast for the focal elements, and decrease it for the rest (you pulled this off real nicely in the last panel on page 8 BTW!). But that's just one way, and I'm sure you can figure something out that suits your style and preferences!
Also, with regards to lettering, I would avoid doing something like the bottom of page 2? The balloons must be read downward, then my eyes have to travel up to get to the next one within the same panel. IMHO, it's best if the eyes don't have to go up to find the next balloon even in different panels on the same page! (though maybe that could be just me XD)
So yeah, I would definitely recommend thumbnailing, and figuring out balloon placement while thumbnailing.
You don't have to review mine, but if you want to review it or just check it out, it's Heart of Keol. It doesn't seem like a fair exchange since yours is only 8 pages so far, and mine is well over 100 XD;