Name them? You're always at the mercy of your randoms, and any good competitive FPS is going to rely heavily on team work, which you never find in a game full of randoms.
As for why Valhalla can work in Halo 4.
-The DMR does have supreme range, but all I see is people saying "gonna get pounded from the hill!", well you can fire back at the same distance with your DMR, and now you don't get knocked out of scope.
-The ordnance system will force players to move around the map, as Over said, no more waiting on the laser to spawn at the top hill every time. I think the ordnance system will benefit BTB more than any of the other playlists.
-People are too quick to blame the DMR for all of Reach's BTB problems. It certainly didn't help, but the maps, more than anything ruined BTB. Blood Gulch is an open field, Boneyard had huge stretches of open field, and Spire was an uphill battle in Invasion, and never had any business being in BTB. Headlong/Ridgeline were not as prone to the DMR wape fests the other maps were known for. Valhalla has a ton of caves, rocks, hills, & a pelican to break up sight lines. It's not like you can spawn in the base and start pinging the other base like Hemo.
Add in sprint, faster movement, and higher jumps, and really, I just don't think you can take your Reach BTB experience and think it's going to play out the same way in 4.