First and foremost I want a real Quarian Engineer. none of this "Quarian Mage" fire and ice nonsense. Let me have a quarian who can command ALL THREE types of drones (Combat Drone, Sentry Turret, and the self defense drone Tali has in 3.). At once!
Then for the quarian infiltrator, get rid of the sticky grenade and let her have Energy Drain and Sabotage.
Secondly...keep the RNG. Otherwise we'll just get the specific loadouts we want immediately then have nothing to work towards.
Thirdly, keep it FPS, but for customization, let us actually choose armor pieces, not just color. I'm not saying let every species have Shepards modular armor, but like, let Quarians choose different hoods, fabric patterns, wiring arrangements, visor visibility, etc.
4th, let us have a place to "hunker down". I hated how they patched the stages so now you can't just hole up. I don't like having to constantly run around, its mindless. I like the tactical benefit of holding a position. Before it was kind of broken, I admit, but once they added units like dragoons, geth bombers, etc, it wouldn't be as broken.
5th, un nerf the Revenant back to ME2 levels. Keep the distinction between the two heavy machine guns as "one fires faster with a larger spread, better for being a huge wall of fire for large targets and crowds" while the other (the n7 minigun) "takes a while to start spinning, but with a more focused, tightened spread". I LOVE my revenant, even nerfed, in ME3.
6th, give us real support classes. Engineers shouldn't just be "shoots damaging spells instead of damaging bullets". Like the Talon engineer was great, decoy is great, sentry turrets are great, thats on the right track, but give more like the trip mine, stuff to control the battlefield, less shooting ice and fire, or at least deploy them in more creative ways, like icing the terrain to slow enemy units, creating firewalls to deter and reroute enemy forces, etc.
7th, buff Armor abilities. Like Sentinels tech armor. Right now people prefer to detonate, but that should be a last resort. As is, most Sentinels arent really any more durable than anyone else, which defeats the purpose. The Geth Juggernaut, a Soldier, is the best Sentinel in the game. We need more "tanks" that sacrifice firepower for defense.
8) Mercs as additional enemy units. Either fighting Blood Pack, Eclipse, and Blue Suns all together, or making them each their own enemy type. Maybe like, Blood pack is vorcha with flamethrowers, the attack dog things, Krogan who rush in for melee like ME1, and Krogan Warlords (like the playable hammerguy) who also use biotics. Then Eclipse....I don't remember what they did. Lots of Tech Armor and Mechs, right? So thats several types of units right there to start with (Sentinels, Saboteurs, turrets, mech dogs, mech soldiers, atlas mechs). Then Blue Suns is a mix of various races, with an emphasis on standard firepower and biotics.
9) Additional gameplay modes. Maybe some kind of "conquest" game type with huge maps where we go from objective to objective with endless enemies, where the idea is to make it through the hordes for the objective, rather than just fending off wave after wave. I'm picturing Battlefield sized maps with Dynasty Warriors/Dead Rising size mobs of enemies.
10) let us choose our type of Omni Blade as an additional loadout option under "weapons".