some suggestions:
1- a conter on how many enemies are left
2- maybe a feature that makes people want diversity in their team? like, 5% more damage if you have just a knight and a thieve in the same team or something like that.
3- maybe a feature where if you go too much right/left there will be a spike wall or something like that where your team can push enemies/enemies can push your team to deal damage.
and is there going to be multiplayer in the future?