All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Al-Munkar (forbidden and evil deeds) is failing to do what Allah and His Prophet have absolutely ordained us to do or doing what Allah and His Prophet have absolutely forbidden us from doing. An example for the first situation is giving up the prescribed prayers, and for the second situation is committing Zina (fornication or adultery).
However, there are no medium acts between good and bad deeds unless one means by medium acts the acts that are permissible for which there is no reward and no punishment, like eating, drinking and the like. Some good deeds are obligatory like performing the five obligatory prayers and other obligations, and some are desirable such as performing the Dhuhha (forenoon) prayer and the like. On the other hand, some bad deeds are forbidden like consuming intoxicants and some bad deeds are dislikable like praying supererogatory prayers after Asr prayer.
It is also known that the more forbidden something is the worse it is and the more required something is the better it is. So, disbelieving in the Oneness of Allah is the worst matter of all and sacrificing one’s soul for the sake of Allah is the best deed of all. Indeed, all sins can be forgiven except disbelieving in the Oneness of Allah and Jihaad (fighting for the Cause of Allah) is the top of the hump of Islam.
Allah knows best.