Whatever adjectives you use to describe religions that are not Islam: degenerate, perverted, unclean, not teaching morality etc. According to Islam, previous revealed religions were sent from God through his messengers; and that with every nation prior, that message became corrupted, twisted and ultimately changed. As a result, any morality those religions might have instilled has since been lost because they have strayed from God's purity. Hence the necessity for God to send another messenger.
Conversion by force, cultural genocide, slavery, marriage to and sex with children, treating women as chattels, war.
Basically, anything you'd view as horrible if it were done by non-Muslims to Muslims.
Non-Muslims.