Are al-shabab good or bad

The term al-shabab literally means "the youth." It is apparently a fairly common term used to name Arabic football (soccer) teams. good, bad, or indifferent will depend largely on which specific manifestation of al-shababyou mean.

There is also a Somali Islamist Terrorist Organization called Al-Shabaab that you may be referring to. They butcher innocent civilians, such as what happened in the Kenyan Mall Shooting; they amputate limbs of prisoners; and imprison and murder both political and civilian enemies. These acts are typically seen as bad, so it is reasonable to call this Al-Shabaab bad.