Where to begin...
Might as well get combos out of the way. Simple physics based combos need to return, which will help alleviate some of the "Michael Bay Effect" from ME3 gameplay. Think Pull and then Throw from ME2. Combos should not be the only damage dealing category to scale with enemy level (if enemy level scaling remains, which is a good bet). What would be nice is if cross class combos were the best, rather than in class.
Adrenaline Rush (and time dilation in general): it might be time to retire the time dilation mechanic from single player. It does not mesh well with MP, and is actually somewhat annoying for someone who wants to jump between modes, IMO. There are many other buffs that this power could give a soldier other than time dilation. Marksman could be potentially changed to an evolution of ARush, with more modest buffs.
Tactical Cloak - if it is going to retain a damage buff, it needs to be more limited in application to one or the other of weapon or power. It also makes sense to revisit the idea of giving free power use at base, which basically imbalances any powers the infiltrator has in common with other tech or combat classes. In very general terms, the ME2 version was more balanced than the ME3 version, which is why in that game many times it made sense to level up other powers like Incinerate before TC. Also, if you break cloak with weapon fire to get the damage buff it should cost the full cloak cooldown (assuming scaled cooldown returns).
Shockwave - I agree with the poster who liked the ME2 version better, which is more of an indictment on how poor the ME3 version is, especially before mega buffs.
Nova - This power should not exist. At most it should be an evolution of Shockwave that changes it from a longer ranged, linear attack to one that radiates a shorter distance from the player in all directions.
Sabotage - It would be nice to turn this into an actual debuff power that affected enemy weapons in some way, either overheating them briefly like in ME1, or giving them an accuracy debuff. I was also not a huge fan of rolling AI Hacking into this power, mainly because debuffing synthetic weapons is better than hacking anyway.
Various tech and combat powers - more radius available. Incinerate was better in ME2 when you could get a decent radius. The Heavy evolutions need to be appropriately powered though. It also makes sense for radius to be a late evolution rather than an early one.
Stasis - enemies should not take damage in stasis without a late evolution
Blue Shields vs Purple Shields - there should only be kinetic barriers, and different powers could supplement them (Shield Boost, or Barrier).
Ammo Powers - The reason they are powers is likely because it is hard to imagine decent actives for the combat classes, but this is not insurmountable. I would prefer that these become gear items, like in ME1 essentially.
Grenade Powers - Again, I prefer a more ME1 approach to grenades. Also, the ME1 grenades felt more futuristic.
Sentry Turret - a poor man's Combat Drone. Not needed.
Tech Armor - ME2 like function. Don't bring back squad cooldown reset (which was supposed to be removed from ME2 anyway).
edit: There are various MP powers which are absurd and I did not bother to mention. AF I am looking at you.