I'll miss nothing about Black Ops. To me, Treyarch added nothing radically different to the game; Modern Warfare 3 brings varied Strike Chains and Point Streaks, the latter is most notably an improved reward for going for the objective.
Black Ops did have a better voice quality when using a microphone, and had a quicker method for joining/inviting to parties, but these were necessities, and I believe that Modern Warfare 3 would have implemented the same things, even if Black Ops hadn't.
MW3 will have locale only search as well as ping matchmaking rather than "Find match quality"
Even XBOX 360 had issues with terrible matchmaking and host selection. Last time I played BLOPS, most of our lobby were Aussies and Kiwis apart from two players who were from Sweden and Netherlands.
Apparantly with using locale only, the host was given to the Swedish and we all dreaded the 1 bar connection.