There will be stabbing in Halo: Reach, lots and lots of stabbing.
There are days that blasting a guy with a Needler or zapping him with the Spartan Laser just isn't satisfying enough, but have no fear, because Bungie has you covered with the inclusion of dozens of assassinations in the upcoming Halo: Reach. The assassinations in Reach are performed by holding the melee button down behind an opponent, which triggers a short animation where the camera pulls back to a third-person view, and the target is killed in some elaborate way.
In a post on the Bungie community blog, Eric "Urk" Osborne said that the assassinations that had appeared in the Reach beta had been just a small sampling, and the animators had included over forty in the final product, with most designed with multiplayer in mind, but a few that are exclusive to the game's campaign mode. Osborne also said that the assassinations were context sensitive and would depend not only on your position relative to your target, but also on the weapon in your hand.
As the assassinations are nothing but showboating, I can see them being the cause of a great deal of rage quitting as people grow weary of getting repeatedly stabbed in the neck. But for those Halo fans who wanted to add a little spice to their multiplayer experience, this seems ideal.