*Post edited because I misread some stuff and didn't know what I was talking about*
I think limited customization of powers might work, in fact it might help to make some of the characters who are currently unplayable in higher difficulties a little more competitive. Like.. maybe I could spend a respec card or something to swap out the lift grenade on my Krogan sentinel for one of a limited range of alternatives (like another tech power, big fat engineer away!)
I think adding more enemies might be difficult because there really aren't any other enemies in the game, it sounds like something which might happen after single player DLC comes out. In the meantime though, maybe some kind of super-enemy for each faction who doesn't appear in every game but maybe gives a reward (like more credits) if you manage to kill him.
Though I have to say that I'm not a fan of raising the level cap.
My fixes would be:
* Biotic combos should be for taking down barriers and wiping out groups of weak enemies, not a universal answer to any situation. They should also be dependent on warp like in ME2, "lift" + "throw" does not need to cause an explosion and it isn't lore-friendly for it to do so, not to mention the constant booming gets annoying.
* Make high powered weapons weaker against shields and barriers, and make rapid fire weapons slightly less useless against armour. Right now, the metagame massively favours single shot high powered weapons over assault rifles and SMGs.
* Give the soldier classes something meaningful to compensate for the loss of ammo powers in multiplayer.
Ultimately, I want to feel like I have to rely on my teammates more, particularly on higher difficulties.
Also, story/objective based multiplayer would be kind of awesome. It doesn't have to be fully voiced or terribly fleshed out, but an alternative to waves would be pretty cool. Heck, even taking the single player maps, toughening them up and getting four people to fight their way across them would be a change.
