Aliens can shoot through walls, you cant. Throwing grenades is a coin flip. You can be out in open fields (no obstruction in any height level) and the grenade might drop right in front of you (even for the most accurate soldiers). You shoot an alien in the back, he shoots you back instantly and kills you. Many other annoying details like this during combat, that make the constant saving and loading unavoidable.Non-combat aspects of the game are great.