What were the three complaints people had about the roman catholic church in the early 1500s?

The "rotteness" of the Roman Catholic Church was at the heart of Martin Luther's attack on it in 1517 when he wrote the "95 Theses" thus sparking off the German Reformation.
In 1500 the Roman Catholic Church was all powerful in western Europe. There was no legal alternative. The Catholic Church jealously guarded its position and anybody who was deemed to have gone against the Catholic Church was labelled a heretic and burnt at the stake. The Catholic Church did not tolerate any deviance from its teachings as any appearance of ‘going soft’ might have been interpreted as a sign of weakness which would be exploited . Its power had been built up over the centuries and relied on ignorance and superstition on the part of the populace. It had been indoctrinated into the people that they could only get to heaven via the church.
This gave a priest enormous power at a local level on behalf of the Catholic Church. The local population viewed the local priest as their ‘passport’ to heaven as they knew no different and had been taught this from birth by the local priest. Such a message was constantly being repeated to ignorant people in church service after church service. Hence keeping your priest happy was seen as a prerequisite to going to heaven.
This relationship between people and church was essentially based on money - hence the huge wealth of the Catholic Church. Rich families could buy high positions for their sons in the Catholic Church and this satisfied their belief that they would go to heaven and attain salvation. However, a peasant had to pay for a child to be christened (this had to be done as a first step to getting to heaven as the people were told that a non-baptised child could not go to heaven); you had to pay to get married and you had to pay to bury someone from your family in holy ground.

Hope this helps a bit :)