One left:
#24 Guessed by The_Liquid_Laser: Return to Zork
#23 Guessed by The_Liquid_Laser: Fire Emblem Radiant Dawn
#22
a) This is the first entry in a series, where you command a group of units through various missions.
b) Steal… *ahem* research the technology from defeated enemies.
c) Missions are turn-based, but outside the mission you manage your bases, troops, equipment and funds in real-time.
#21 Guessed by Darashiva: Deus Ex: Human Revolution
#20 (kinda) Guessed by The_Liquid_Laser: Fire Emblem Awakening