Of these I bought Underdark, PHB3, and Hammerfast. I have not used any of them yet (since we're not yet regularly playing 4e).Underdark (January)
Player's Handbook Races: Dragonborn (January)
Martial Power 2 (February)
Hammerfast (March)
Player's Handbook 3 (March)
Did you buy them? Did you use them? Did they change your D&D campaign?
Looking back on them, which were the hits and misses of the first lot of D&D in 2010?
Hammerfast was probably _the_ best D&D product I bought in 2010. 'The Plane Below' being a strong contender. I liked the latter more than 'Underdark', though that is also a very good book. Similarly, I liked 'The Plane Above' a lot.
PHB3 contains a lot of great stuff (monk, seeker, skill powers) and a lot of meh stuff (psionic & hybrid rules), but overall it's still a good book, imho.
The books I'd consider misses are the ones I didn't buy
The biggest disappointment in 2010 was the 'Essentialization' of 4e. It's similar to what happened when I started my 3e campaign: A month after we started playing, the first 3.5 book was released. Very annoying, since I don't buy half-editions. So, I'm again in the place that we're going to play with a ruleset that is already 'deprecated'.