I've been watching the Xindi season again for the second time and I can't see why it is always dogged on. It's not that bad. Don't get me wrong....the Dominion story arc of DS9 was better but still.....the Xindi staory arc isn't that bad either.
The only complaint I have with the Xindi arc is how it all began. If you super weapon isn't quite ready....why use your primary target as a test? That would be like dropping the Trinity bomb on Okinawa, Japan before dropping the bombs on Hiroshima and Nagasaki during WWII. Why give your enemy a heads up?
Now there were some slow moments during the season but considering that long stretching story arcs are not a trademark of the Star Trek Universe..I think they did ok with it.