Guild Wars 2

GW2 could have a dungeon or instance which a group of 5 players would have to hold some ground while mobs try to invade (something like the guild mission).

Each wave would get harder and harder with diferent enemies mechanics (to make every class playable) , and at the end of each wave a boss would come giving increasing silver/gold/dungeon token (for example.. 1st boss 5 silver/1 token, 2nd boss 10 silver/2 tokens, 3rd boss 15 silver/3 tokens…)

Build and upgrade some structures to help defending the spot. Choose damage or crowd control, single target or area… like the tower defense games.

Also could have some level scaling (like fractals) so bad players dont get carried by good players and good players dont get penalty for having bad players in the party… So everyone would have to grind their abilities to earn good teams.

Could have some themes like defending an asuran instalation, protecting some quaggans etc etc…

I really like defense-like stuff and would love a dungeon in this format.