As a Death Knight main since the minute I logged into Wrath of the Lich King, my most fun times were when I was specced as Frost. I just loved everything about it, the feel, the theme, the playstyle; hitting things with a big ****-off two-hander for massive damage was just so much fun. But at some point, the developers decided that having a Death Knight spec that could dual wield properly was more important than keeping my playstyle intact, and so they made Frost the dual wield tree. In doing so, they ruined my favorite thing about being a Death Knight, and for over a year since then, I've been Unholy.
But they're going to redeem themselves in my eyes. When the developers decided to turn Blood into a purely tank-based tree, they also realized that some people would miss having a 2H DPS spec that wasn't reliant on a pet, and so, they decided to bring two-handed Frost back. The knowledge that my favorite spec is being brought back, that it will finally once again be a viable option for DPS in raids, is what I'm most excited about.
Oh Frost Strike, how I've missed you...