OP,
This truly saddens me. It seems that you are not alone. From my readings on the matter it appears that there are many others in the same state. I wish I could derive an answer in just a few short words but this game waaaaay harder than a simple hack and slash. If I could give one piece of advice it would be to backtrack your steps leading you to the Tower and clear everything. Do all the quests you can in the other areas leading up to this epic battle in order to level your party and have an easier go of things.
All,
I know most of you are pros but I am wondering what you think would be the response to a Combat Guide (not a walk through, not what is termed a Strategy Guide). I am so in love with this game that I would love to be able to construct a guide that would allow others the joy that it brings me. I have been playing this type of game since Wizardry I and the time when D&D Red Box was black and find myself on the other end of the spectrum (wishing there was less OP'd in the game).
Zaedar's Golden Rule #2 - Leave no stone unturned
Zae