These maps came out quite awhile ago, and I planned on waiting until they were free, but after hearing they won't be free ( at least for awhile ) I got them just today.
Avalanche: 4.25/5 Huge map, with man cannons to make it seem less small and help you travel, but - meh. There are vehicles at the spawns on this map, but - it's just not that great. Cool design, but too big, and not the most epic of battles. Avalanche isn't bad, but I thought it'd be a lot better than it actually is.
Black Out: 4.75/5 A remake of the classic Lock Out from Halo 2 - yeah, I bet you didn't know that. Black Out is a great map for Team Slayer as well as Team SWAT. Great map, and is actually better than the original map - wow.
Ghost Town: 4.5/5 A map many people thought would be terrible before the pack came out, but surprised most, including me. Ghost Town is a fantastic map. It's asymmetrical, ( If you don't know what that means get the hell out. ) and it just has a great look to it. It's medium size, and fun to play on. A lot of fun - great for most game modes.
For $10, you get these pretty damn good maps, a 3-month subscription to Bungie Pro ( Meh. If you don't know what that is, it doesn't matter. ) and the ability to finally play Team SWAT whenever you want. I must warn you, though, Team SWAT doesn't play the same was as in Halo 2 - it seems harder... for whatever reason... still, you can't really go wrong. I'd say buy it.