Grisaia no Meikyuu: Caprice no Mayu 0

They both have male protagonist characters who show an exceptional ability to kill people. Grisaia's protagonist is more inhuman from a cruel, abusive, abnormal past. Both shows show the protagonists training how to kill people in both guns and knives. They both have their protagonists put into morally ambiguous circumstances, with a stronger case being able to be made that they are, the bad guys (for at least part of the series). 

The anime have different themes and audience but they share similarities. Both anime are about a MC which has a really sad past, which have made them 'cold' and is a main factor for killing enemies in cold blood. They both also kill to protect the people they love. 

Both shows detail the life and transition of a mercenary to a high school student. While Full Metal Panic! has more of a comedic undertone, both shows have a decent amount of action, violence and blood. Grisaia takes more of a harem/romance path, both shows are quite similar in regards to the MC. If you liked Full Metal Panic! Grisaia will not disappoint you; it takes much more of the mature and darker route that Full Metal Panic! did not quite touch on. 

drama in grisaia no meikyuu and grisaia no rakuen (sequel) is pretty similar to drama in angel beats when the protagonist is stucked by rocks and hungry. 

Side stories telling the past of a character that are darker and much more interesting than the main series.