I bought the first trade, and hardly consider it "unreadable." I liked it enough to get the next one at some point. It wasn't as strong as Midnighter(/Apollo) or Supergirl*, and perhaps not as exciting or big as a title with "Justice League" in it should be, but it's not remotely painful. I think from Priest's first issue his run will likely be better, but as far as unnecessary team books with Batman in them go, JLA is better than others.
*Supergirl is another one I've seen people complain about being bad, but I've yet to see anyone articulate why in a satisfactory manor.