I used Throw a lot, especially on insanity. It recharges instantly and disables a foe for a few seconds, potentially a whole group. With the right character you smash through armor/shield really fast, but some opponents regenerate health quickly so it takes more time to take out health. So what you do is you just break their armor/shield after which you throw and move on to tear down the next. Throw is homing and needs nothing more than hurling it and when it hits it do damage to nearby opponents.
Whenever you face organic enemies, bring Jacob or Grunt with Squad based Incindiery Ammo. No regeneration. I always do that. Also, I always bring someone with Squad based Disruptive ammo (i.e Zaeed) when facing synthetic enemies. Basically stun locks them, allowing your NPC followers to do all the killing without breaking a sweat.
Even Insanity is smooth sailing with a little preperation.
You may ask, "why don't you just shoot them, they have no armor"? Because while shooting you take damage, both from the one you shoot at and the others nearby. It's more effective to quickly blast armor/shields and then disable the foes than blast armor/shields/health one by one.
Maybe we're playing a different game. Exactly what enemies are solid with no protection, yet have fragile protection (except those blasted Husks that I consider so annoying)? Most enemies I've faced that were worth talking about - Commandos, Vanguards, Mechs, Geth, Harbinger, most Collectors etc - have rock solid defenses, but are killed with a few shots once they only have their health bar left. In fact, taking down their defense is the whole fight - once that is done, NPCs with a little firepower (Zaeed, Legion, Thane, etc) will take out enemies really fast.
Also, damage on a foe on the ground takes far more damage from a shot. Why waste ammo?
Just remember to switch weapons a lot. Picking up ammo will restock all your weapons, so if you empty every weapon you have, you still only need a few ammo clips to fill it all up again. The only weapon I actually run out of ammo with is the Sniper Rifle, because I tend to use it way too much, as it kills so redicilously fast. Other than that, I just keep juggling the weapon type and am never in any danger of running out due to how the ammo clip system is designed. You litteraly get 3 or even 4 times as much ammo per clip if you just juggle enough.
An example to those who find it hard to understand the ammo system:
- You start the fight by taking out 3-4 rocket troopers in the back with a Sniper Rifle.
- You continue by taking out some mid-range people with an Assault Rifle.
- The few enemies that are left, actually made it fairly close, so you blast them in the face with a Shotgun.
All you need at this point is two ammo clips and you're back to 100% ammo with all weapons, since they all regenerate as if only one of them had lost ammo.