Eh, that's only with 1v1 encounters. Longer encounters allow firefights to be a little more interesting, make it so each player has enough time to demonstrate more skill than the other player, and doesn't turn the firefights into who sees who first. But something shorter encounters allow for is clutch plays where someone can be outnumbered but come out on top. In CoD someone with quick aiming and maneuvering take down multiple people with nothing but the gun they spawned with. Now I think CoD's encounters are too quick so that it does boil down to who sees who first and taking out multiple targets is much too easy (one guy keeping his sights on a doorway can mow down person after person no matter how many rush through).
I thought the encounters in Halo 3 were fine and if anything edged on the too long side but with Reach they took it to a whole new level. Not only do non-power weapons take more bullets to put someone down, you have to artificially slow your RoF to make sure those piles of bullets necessary actually land, and the clip sizes have been reduced to force players to reload in combat much more often. Then there's the power-weapons that instead of getting nerfed alongside the primary weapons actually received a buff in almost every instance. This has turn the game more into who has the power weapon than it ever was. No longer do I have a shot at BRing the guy with rockets as long as I jump over the first, I'm not going to put the shotgun down when I'm in it's now huge range, and if the sniper somehow manages to miss my slow moving ass then they should've stuck with the AR.
What gets me the most though is whether or not long encounters require more skill, first and foremost they should be more fun. Long encounters are fun when players can maneuver all about during the firefight, jumping up and over crates, moving from one level to the next, strafing quickly around columns, etc. But with Reach they nerfed maneuverability during firefights, the base player speed is reduced, and the jump height is embarrassing. Now firefights just consist of long stretches of players skating around the floor pulling the trigger until someone's down. It's more frustrating than fun. Maybe they really will change these attributes by release but I think my concern is justified.