Starting at the upper commander levels and on into captain and admiral you encounter engineer type mobs that have that ridiculously overpowered shield recharge ability. Not the one castable on others, but the self-only one that makes you prettymuch unkillable.
Whenever I encounter a group with such a mob, I naturally have to kill it last because of the ridiculous amount of time it takes to actually down one, even with myself and all 4 of my Boffs all focus firing on the guy, he simply recharges his shields to full every few seconds and takes virtually no damage. Most of the time when I kill these guys, they're shields are still at full strength and the only reason they died is because of the very minor damage that bleeds through shields over the course of a minute or so of constant shooting at him.
This adds no challenge to the game, at no point is my group in any danger of dying, it is simply an irritating and time consuming encounter.
I have started loading up all 4 of my Boffs with stun phasers just to maximize my chance to get an Expose on these guys, but expose is still few and few between even with 4 BOs with stun phasers and 3 players on my team using tactical powers to cause exposes.
Furthermore, even when the target IS exposed, and I use my exploit sniper attack, even from behind for the extra flank damage, it STILL doesn't 1-shot the guy like it does every other mob. He survives and recharges shields to full once again.
I've also tried respeccing my science officer to remove one of her healing abilities and replaced it with Tachyon Harmonic since it's supposed to do a lot of damage to shields, but even with 9 points in the skill it's not enough to punch through these overpowered shields.
It's absolutely ridiculous. Expose + Exploit + Flank, anti-shield powers, and even melee attacks, and the guy just stands there and tanks it for at least a full minute before finally dying and in some missions theres one of these guys in nearly every group of enemies.
There needs to be some kind of decent way to counter this crap. I've gotten to the point where I just IGNORE these retarded mobs and let them continue to chase me and fire on me with their negligible damage while I complete the rest of the mission because they simply aren't worth the time it takes to kill them.