We sat down and played a Fed v Klingon Ambush, with Feds as defenders, this weekend. 2 OCLs and a Constitution-Class against an F5 and a D6. Klingons took down both the OCLs, but it was noticed that the Feds have really quite excellent fields of fire. The F5 managed to warp away in time, but the D6 got crippled and taken out by the Heavy Cruiser.
I guess the takeaway lesson that we got is the Klingons can be very powerful but it's all about their movement and presentation of the forward shields - one torpedo hit on the rear arc of the D6 from an OCL that was able to pull of a high enery turn all but doomed it and meant it had to fight a rearguard action while the F5 limped away to get fixed. I'd post a report, but I can't remember any exact details of criticals etc - I know that the Klingons were luckier than they should have been as they wiped out an OCL on turn 2, and the Federation were very unlucky until that one HET whipped an OCL round to take out the D6 with torpedos.