I have not played Klingon in Headstart yet so I may be ahead of myself here.
In OB when you leveled up a Klingon character all you got was a Klingon sounding voice saying "Qa'Pla"
Thats cool and all but may I suggest, if possible without copyright infringement, getting the voice piece from DS9 of Gowron saying "Honor to you, and your house."
He says it in that badass Gowron voice, and he is handing out awards and medals to people as he says it so it would be an appropriate thing to say. And if it can't be Gowron then have whoever does the Qa'pla voice over say the line.'
What sucks is I can't remember what DS9 episode that was.
EDIT: I said Martok, I meant Gowron. Got my Klingon characters mixed up.
Just speaking for myself, I actually rather liked the level up noise for Klingons. Rather understated.
If they're doing more voice recording, the #1 thing I would most want to see is the addition of bridge chatter in combat. I would love to hear "Red alert! Shields up, arm phasers, load all photon torpedo bays." when combat starts, "Hull breach on deck seventeen! Containment fields are holding." and "Casualty reports coming in from all decks!" when my ship takes damage, and "Direct hit! Enemy shields down to forty percent." when I fire.