I play a lot of Rook and have generally done fairly well. Typically my first skill is lvl 1 towers... and that's the only point I put into towers.
Boulder+Hammer is effective if you can time it right but Hammer Slam has it's uses otherwise. It's extremely useful on creep waves to gain quick experience when on the move for instance. It's also very effective at simply scaring enemy demigods off and giving you a little breathing room. Many will start to run as soon as they see the hammer go up and it's easy to stop the slam when they do, making it easy to keep it around as a constant deterent to some gank manuevers. Do not throw the hammer the second an enemy demigod gets in range either, they'll often waste their stun right away thinking you will - meanwhile you just slap them around instead and hammer after.
I'm not arguing that a tower Rook can't be good or very effective, but it's certainly not the only viable way to play the Rook.
-dolynick