Has potential, but needs a bit of work. Rather than going back and explaining in posts how things work (like the immunity to acid, or using a rope) actually mention it and describe it in detail in the chapters. It'd make things easier to follow and save you the time from writing explanations.
Also, I actually think the style is promising. Jordan, as you may or may not recall (Dunno if you've read the book) Bram Stoker's original Dracular novel was in a similar style- letters and diary entries. This reminds me of a diary-style fic, which are hard to pull off but can be good.
And to save asking, Jungle Scrabs were a protoype concept I thought of long ago. I considered how many animals in the real world have different subspecies, and rarely stick to 1 environment- the many forms of big cats, or apes, or bears, are good examples. So I figured it's not unplausible to suggest the same for oddworld, hence the Jungle Scrab. Slightly smaller and slimmer to enable more lithe movement in the clustered terrain, skin shading to green for better camouflage, and a tendancy to stay truly solitary (as opposed to the Desert/Plains Scrabs which of course ocasionally form AlphaScrab herds) with rigid territories.