When I heard of large open ended endings, along with this will be the end of "Shepard's Story" while still keeping the world of ME open for future stories, I thoughts the endings would be something like this;
Notes: ME3 War Assets and Crucible are still critical to the storyline. The Citadel is still ends up in earth space and the Crucible still links to the Citadel but there is no ground war, all the fighting with everybody happens on the Citadel. The Crucible works by sending a signal that disrupts the Reapers internal processing and communications, weaking them. The War Assets are required to protect the Crucible. The lower the assets, the more damage it gets before it fires. The more damage it receives the more damaging the fire pulse is to those other then the Reapers. The War assets are used as ships to protect it, and ground troops used to fight thru the Citadel faster.
1) Shepard critically fails, Reapers advanced throughout the galaxy impeded. (like the "fake" ME2 Shepard is dead ending.)
2) Shepard scarifies Earth and himself, but stops the Reapers at a major cost -- all current civilizations will take 100-300 years to recover, the Humans, Krogan, Turians & Quarians take the brunt of the loss, and are hanging on for survival of the species. 75% of Shepard's team has perished.
3) Shepard keeps Earth while stopping the Reapers, Depending on player actions in ME3, either Krogan and/or Quarians are a dying race and hate Shepard/Humans. 50% of Shepard's team has perished; 50% chance Shepard will have died too.
4) Shepard keeps Earth & stops the Reapers, but at the cost of a impending galactic war that not even Shepard can stop; 25% of Shepard's team has perished.
5) Shepard rolls a 20 and Reapers are stopped dead cold. There is a uneasy peace, but so far everybody is still happy shooting at the reaming scattered reapers as long as Shepard keeps the races "united" in peace. All of Shepard's team lives and we get to see blue Shepard babies (or what ever baby producing couple the player developed).
In all endings (2-5) Shepard is a Hero. Regardless on how you end ME3 (2-5), you can start ME4 200 years after ME3. Endings 4 & 5 still have a galaxy wide war, either after Shepard dies or Shepard dies in trying to stop, which severely weakens everybody. Endings 2 and 3 has the galaxy still very weakened recovering from just barely surviving the Reaper threat.
So other then a few wording tweaks at the very start of the story - you have generic ME4 perfectly set up after ME3. The story: The Reapers may be dead, but all the technology they left behind is still raging its own hidden secret war. What remains of a splinter cell of the Geth, along with other organics still indoctrinated (and their childrens children) during the attack 200 years ago are trying to develop a method to spread the indoctrination signal throughout the whole galaxy and bring to fruition "Reaper 2.0."
Notes: ME3 War Assets and Crucible are still critical to the storyline. The Citadel is still ends up in earth space and the Crucible still links to the Citadel but there is no ground war, all the fighting with everybody happens on the Citadel. The Crucible works by sending a signal that disrupts the Reapers internal processing and communications, weaking them. The War Assets are required to protect the Crucible. The lower the assets, the more damage it gets before it fires. The more damage it receives the more damaging the fire pulse is to those other then the Reapers. The War assets are used as ships to protect it, and ground troops used to fight thru the Citadel faster.
1) Shepard critically fails, Reapers advanced throughout the galaxy impeded. (like the "fake" ME2 Shepard is dead ending.)
2) Shepard scarifies Earth and himself, but stops the Reapers at a major cost -- all current civilizations will take 100-300 years to recover, the Humans, Krogan, Turians & Quarians take the brunt of the loss, and are hanging on for survival of the species. 75% of Shepard's team has perished.
3) Shepard keeps Earth while stopping the Reapers, Depending on player actions in ME3, either Krogan and/or Quarians are a dying race and hate Shepard/Humans. 50% of Shepard's team has perished; 50% chance Shepard will have died too.
4) Shepard keeps Earth & stops the Reapers, but at the cost of a impending galactic war that not even Shepard can stop; 25% of Shepard's team has perished.
5) Shepard rolls a 20 and Reapers are stopped dead cold. There is a uneasy peace, but so far everybody is still happy shooting at the reaming scattered reapers as long as Shepard keeps the races "united" in peace. All of Shepard's team lives and we get to see blue Shepard babies (or what ever baby producing couple the player developed).
In all endings (2-5) Shepard is a Hero. Regardless on how you end ME3 (2-5), you can start ME4 200 years after ME3. Endings 4 & 5 still have a galaxy wide war, either after Shepard dies or Shepard dies in trying to stop, which severely weakens everybody. Endings 2 and 3 has the galaxy still very weakened recovering from just barely surviving the Reaper threat.
So other then a few wording tweaks at the very start of the story - you have generic ME4 perfectly set up after ME3. The story: The Reapers may be dead, but all the technology they left behind is still raging its own hidden secret war. What remains of a splinter cell of the Geth, along with other organics still indoctrinated (and their childrens children) during the attack 200 years ago are trying to develop a method to spread the indoctrination signal throughout the whole galaxy and bring to fruition "Reaper 2.0."