I read that there will not be a Shepard in ME 4. Which I think is the right call... So do away with the Reapers... and The Collectors...
and start a NEW EPIC SAGA
A new threat! What could be more hardcore than Reapers though? Especially since the ending of ME 3 was a bit of a "hasty exit" to an otherwise FANTASTIC concept. Can you realistically have a continuation?
I mean... earth is a little toasted. The Asari planet is very well toasted... The Turian Planet took a beating, and I think the Krogan planet was slightly improved.
Whatever you chose as the ending... the Reapers have either flown away, fallen down... or burst out laughing.
The T-1000's little nephew convinced our hero to off himself/herself... so we're pretty much screwed in terms of continuity.
But what about the "Dream Theory".
(WARNING SPOILERS AHEAD)
If you killed the Reapers... there's a shot of Shepard's N7 armour stirring in the rubble after the whole red circle of fail... suggesting that the whole citadel sequence was a "Dream".
Should Shepard wake up and be in ME4?
I don't think so... At least... I hope they don't go that route.
What I would do, is employ the formula they used very effectively in KOTOR. Change the time frame, but keep the magic of the universe!
Base it 20 or 30 years in the future! So there can be lot's of tributes to Shepard as a homage to the original trilogy, but enough time for the respective world's to recover and stabilize.
Then you can literally do whatever you like with the story! Have the old ME Trilogy characters rock up every now and then, especially since the groundwork has been laid down for them to survive.
Joker as a Grand Admiral. Wrex as the first Krogan council member. Garrus as the Turian head honcho... Ashley as... you get the idea... and a story can be created in this different environment.
There's space for new intrigue, espionage and drama.
Main Character:
Shepard's child with the love interest?
Someone completely new?
It could just be another soldier in the Alliance who get's put into an extra-ordinary situation... like Shepard was.
New Uber enemies:
Splinter groups like Cerberus still loyal to the Reapers?
The Creators... OF THE REAPERS? I mean... Someone is missing all that biomass that wasn't harvested right?
Prothean cloning goes wrong?
There is potential...
Gameplay:
The Gears of Effect formula should work again, it's pretty effing awesome if you ask me! But PLEASE, no need to make it MORE COMPLICATED. Newer and better doesn't mean you have to add 2 new classes and 12 new powers, weapons and item mods. Since the multiplayer is so effective, use that as a base and stick to simple, clean improvements.
More vehicle control sequences Please!!!
More "Playing as another character/race" during the storyline please!!!
Keep the best parts and refine the ones that are a little shaky.
Best parts:
3rd person combat system is working very well IMO
Powers rock!
Buddy system rocks!
Combat pause system rocks!
The multiplayer is a lot of fun, but we need more game types... possibly including a longer co-op "dungeon" game type. Similar to a single player mission... except it's you and your mates as the squad! Higher level means more difficult missions etc etc.
Good, mature, in-depth storyline, with a good script and feasible moral dilemmas.
The feeling that each choice has consequences and the "Paragon vs Renegade" system is a winning formula.
Romance has become a staple... although it got a little corny in ME 3.
Keep the EPIC nature of the game. The EPIC music, the EPIC landscapes, the EPIC units... the scope and scale of the Mass Effect world made it classy and differentiated it from other games in the RPG genre.
Celebrity voice actors also lend credibility to the game and the characters.
Parts that need tweaking:
Item collection, economy, upgrades... All need to be tweaked AGAIN. this still isn't right IMO.
Somehow make the "mission system" more user friendly. Throughout the trilogy, I found it a bit iffy working my way through the side-quests. It's practically impossible to do ALL OF THEM without consulting uncle google. If the missions had some sort of "Waypoint" feature to at least put you on the right planet... would be AWESOME!
Make upgrades WORTH IT!
That's all I can think of now...