Death Zone was a fun read and a good value at $3.99. The ending is a cliff-hanger, but it's more a setup for the next story in the overall arc and didn't detract from the conclusion of this book. I wasn't able to really connect well with the characters in the story, nor their plights. I don't feel compelled to start reading the next book in the series, but I probably will at some point.
I enjoyed Gabriel's Revenge very much. Steve Umstead did a great job with imagery, both to paint a picture of each scene as well as to shed insight into the story's characters. The characters had a depth and realism that encourages the reader's emotional investment. The socio-political and technological background upon which the story was crafted was believably realistic. The plot itself had some nice twists, including my favorite plot device -- a coming full circle.
Gabriel's Revenge is one of the better books I've read from smashwords, and I definitely plan to check out the sequels.