Its not unwatchable, nothing like that. However it does not add much value to TWD universe. If you see it as a standalone thing, and not a piece of the puzzle, it doesnt stand.
After all the attempts, I have a feeling that the next really good content would have to fast forward untill new fully developed (and yet promitive) societies have emerged, a completely new setting with new opportunities for plots, drama and action. As long as its characters vs other characters in the setting dominated by walkers, I am afraid we have seen it all already.