Actually I found the Firepower pack helped to rebalance certain things on the harder difficulty settings. Specifically, playing as an Adept is really tough on the higher levels since you have no powers that can reliably deal with shielded enemies. With vanilla shotguns it's difficult because the Adept seems to have very weak shields and getting in close is almost certain death. the Geth shotgun remedies that on both fronts.
As for the ME2 preorder DLC; I got the Steam "digital deluxe" version so I've never used the Blackstorm. Looked like fun though. I think I had that fugly Inferno armour, the Incisor (sp?) sniper rifle and the Collector weapons and armour (plus of course, Zaeed & the Normandy crashsite.)
The sniper rifle was actually quite useful if you gave it to your sniper squadmates as it would often completely take out enemy shields in one burst. As a Soldier or Infiltrator I found you have to resist the urge to sight on the head as the recoil will send the second & third shots high. Instead go for the centre of mass and let the recoil do the work and (if you're lucky) get the headshot with the third round. VERY effective vs. Vorcha.
I've actually been messing round with the Gibbed editor recently and just for fun I'm seeing what it's like running around as a Sentinel with the Claymore, the Revenant & the Willow. I'm going to have to up the difficulty to nightmare or something because I'm just single handedly cutting through every enemy, even on hardcore!