Battle for Olympus is still a pretty awsome game. I still sit down for a few hours every couple a months and beat it. Since the save system is such a pain I usually just play it straight through when I have about 3 extra hours on my hands. Some areas still suck though no matter how good I get at the game. Pythia, for example, blows all that jumping from pillar to pillar hoping not to get hit in midair because if you do its almost certain death, and then you have to go back and collect more olives for your best sword. Crete used to suck pretty hard for me too, but its more about memorizing the path than skill. Tarturus is a pretty brutal level and the last boss is a little hard at first, but once you know how to beat him he is fairly easy.
As a side note this game is probably my 5th favorite on the NES behind Guardian Legend, Ninja Gaiden 3, Crystalis, and Blaster Master in that order.