Mass Effect : How It Could Have Continued

Mass Effect,one of my favourite game series but with a disappointing conclusion to it.How I wish that there would be another one or two installments to justify the horrible ending that Mass Effect 3 had.I had an idea that I shared with a friend that could be a continuation of the Mass Effect series by making another game rather than just a DLC; I'm referring to the Leviathan DLC. That DLC was a revelation and it was so important, I feel it could have been a new game by itself. Here's what we came up with :

Backstory: The apex race,calling them Leviathans to simplify things,were the most advanced species of all time.So advanced that they not only manage to dominate this galaxy,The Milky Way,but they dominated other nearby galaxies as well.Being a race so advanced,the Leviathans forced the other less advanced species to work for them and join their Empire (since it was told that things tend to repeat themselves in every cycle,this also happened with the Prothean Empire).But with every Empire there will be a rebellion against it.This rebellion,the Sympathizers,is lead by Leviathans who disagree with the Empire's mission to make servants of the intelligent species that they find.

Leviathan

The Sympathizers seeing the Empire's cruelty towards other species,decided that a race too advanced with overpowering technology is a danger to all other life in the universe.So,they plan to destroy the Empire and also to harvest and preserve life at the same time.The Sympathizers managed to synthesise themselves with technology,life meets machine,to form the Reapers.The most powerful of them was the Harbinger,who was the leader of the rebellion.The Reapers with the help of the other species then waged war with the Leviathans.The Leviathans tried to fight back. They managed to overthrow the Empire, killing and harvesting them to form more Reapers.After that,the Reapers turned on the other advanced species who were helping them,harvesting them too then lurking into the centres of the galaxies,hiding and waiting for the next cycle.

After Mass Effect 3: Harbinger managed to escaped to our galaxy before Shepard set off the Crucible.And because we are not the only galaxy with Reapers,Harbinger has called the Reapers from other galaxies for aid as Harbinger is adamant to continue the cycle.Now a larger force of Reapers,with a whole lot of different assimilated  species from other galaxies as foot soldiers approach our galaxy and with our defenses already diminished,we have to look for more help...

 The New Game: Desperation creeps in,and with the Crucible destroyed, we're working non stop to find something that can help us against the new Reapers.News comes that a species is discovered to have taken down a Reaper..(the Leviathan DLC comes in).We have to get the Leviathans that were in hiding to our side,doing whatever we can to make that happen.Everyone prepares for the inevitable final battle...

3 ways the game could start (depending on your choice at the end of ME3) :

1.Destroy ending(Red) Shepard survives the Crucible blast.Get to continue playing as Shepard.Reinforcements are low.
2.Control ending(Blue) Shepard sacrifices himself to control the Reapers within the vicinity of the galaxy.Get to play a new character(though this sounds like a bad idea) or maybe one of Normandy crew.Have the Reapers controlled by Shepard to fight alongside you.
3.Synthesis ending(Green) Shepard dies,same as the Control ending.Technology merges with life.Able to have better weapons,upgrades and powers but no controlled Reapers to help.

There ya go,this is just an idea far from perfected.