Elder scrolls: I mean if you add all the games togther thats alot of lore and basicly a whole world! It's perfect for the MMO treatment!
Alien vs Predator: I was thinking it would be like a MMO mixed with a FPS kinda like Borderlands (I just got that and it's very fun) or TF2. You could switch between FP or 3rdP. 3 races Humans,Xenomorphs and Predators all would have differnt play styles. You could fly around to differnt planets etc But maybe have to sets off each race kind like theres civel wars happening in each race.
Humans would be trying to survive in space in colonys etc maybe you could choose to work for the army or Weyland Yutande(I can spell that name)?
Classes for Humans
Marine: Basic allrounder DPS can use alot of differnt weps etc
Medic: Heals

Heavy weapons: The tank for humans
Battle android: Being a robot it can use stealth tech so basicly a rouge/warrior mix
Demo: Is a form of DPS that uses bombs etc maybe have a move when low on health nearly dieing they could suicide bomb themselves and do a AOE move XD
Aliens I think would just want to spread themselves like normal and the quest givers would be Queens and Pretorians. When you amke your toon you choose and customise your class then you see a facehugger to it's job and you burst out in all the gory glory! so if you choose a dog Xeno you'd see a dog get facehuged etc. Instead of useing gear like normal races you'd mutate yourself to upgrade like mutate stronger claws etc
Classes
Drone: can be melee DPS or ranged, Useing class and acid spit. maybe other projectiles? Spines?
Warroir: can be a tank or DPS but is sololy Melee so like a fury warrior for dps etc
Dog alien: Fast scout type unit maybe could choose to be stealth aswell. DPS maybe heals?
Predalien: Allout tank class. Better than warrior for tanking, Stronger but slower.
Clucthmother: heals dunno how that would work maybe spits at players to heal them? Could throw facehuggers at foe to stun them.
All aliens would have acid blood that does damage in close combat and all can use their 2nd mouth.
Predators. You'd start off as a youngblood and slowly go up ranks, hunting bigger prey etc. All classes could use stealth but Alien and human plays can find them useing smell for Xenos and Scanners for humans so it's not unfair. Maybe have that race war that is going on in that new Predator movie? with the "super" ones and normal ones.
Hunter (Looks like the one in the first Predator movie): Is DPS, manly Melee class can use a few high tec weps but prefers to use basic weps.
Warrior ( think 2nd movie one): can be melee dps,ranged dps or tank prefers to use high tech wpes than basic weps
Soothsayer: is heals can choose to use herbs etc to heal or high tech meds
Beserker: Big bulky tank basicly

Tracker: a rouger mixed with a hunter uses those hunting dog things
Those are my ideas for MMOs what are yours? Be civil about things here no going "aww thats poopies"