We're most excited for 8.2 because it includes support for Apple Watch and that rumored Companion app, plus new Health app capabilities. But iOS 8.3 packs in some useful features like wireless CarPlay, no Lightning cable required. No word yet on which cars will support wireless CarPlay or when 8.3 will roll out.
According to 9to5Mac, iOS 8.3 also includes new emoji (insert praying hands here) and some other minor fixes like an easier login process for Google users with two-factor authentication enabled. The updated OS also might bring Apple Pay to China, which would add a significant amount of people to the pool of potential mobile payment users.
iOS 8.2 is currently in its fifth beta and is expected to drop in March or April, when Apple Watch is ready to ship, so 8.3 is still a ways off.