The skill tree is what truly diversifies the classes. Each class has a unique skill tree with several branching paths. You can get a new skill every time you gain a level, but you'll never be able to get every skill in the tree. Again, you'll have to choose which skills will best fit your playing style. Take the medic, for instance. One path makes your medic a more efficient fighter, while another increases your medic's ability to treat wounds. If you prefer to take your time and carefully complete each mission, you may be able to finish each one without sustaining any serious injuries to your troops. In this case, you wouldn't need an exceptionally good medic. You might, instead, opt to improve your medic's fighting ability to deal more-damaging critical hits--a random occurrence in battle that inflicts an exceptional amount of damage on enemies. In any case, when a soldier's vitality points are reduced to zero, he or she is merely rendered unconscious. You can't revive characters during the mission, but they'll be alive and kicking in the next one.​