Yes. I actually just a few games ago figured out how the counter the tail. If you think an alien is nearby, then block and then melee him then unload. It's a guaranteed kill. If an alien your are fighting begins to start using his tail, then throw a melee, and do step 1. It's actually really easy to counter unless you didn't know it was there.
This method also stops predators just as well. In fact, I play the marine as a melee machine. Hide around corners, wait for an enemy, then melee them and blast them to death. Its a clean 2 second kill. Doing this method, I actually became a force to be feared myself. The shotgun only helps this even more. Melee, then fire both barrels for an instant kill (not that it doesn't ALREADY instant kill them, which is awesome against predators, because they like to run away and then get you in the next room).
After figuring all the counters out, I'd have to say this game is extremely balanced. One of the most balanced FPS games I've ever played (and Over 9000! times more balanced than MW2).
