• Adds the ability to collect multiplayer experience by playing Horde mode. Players currently gain experience at this rate:
• 50 points per completed Casual wave.
• 75 points per completed Normal wave.
• 100 points per completed Hardcore wave.
• 125 points per completed Insane wave.
• Adds the ability to restart Public Horde from the current failed wave instead of having to start over from wave 1. Title Update 4 also allows the host to kick players from a Public Horde session.
• Increases the frequency of downloadable content (DLC) maps showing up in map voting if all players have shared map packs.
• Adds a message at the end of the match to explain to players that they should wait before quitting so that they avoid an experience penalty for quitting early.
• Adds support for the new campaign chapter, "Road to Ruin."
• Adds 13 new achievements worth 325 points. All of the new achievements require the Dark Corners Map Pack, a set of seven new maps and a deleted campaign chapter to be released July 28. The 13 new achievements are:
• "My Way or the Highway" (25 points): Without being detected, complete the "Road to Ruin" deleted scene after choosing the stealth option.
• "Highway to Hell" (25 points): Complete the "Road to Ruin" deleted scene after choosing the guns-blazing option.
• "Two for the Road" (25 points): Complete the "Road to Ruin" deleted scene in co-op as either Marcus or Dom.
• "Be Careful What You Wish For" (10 points): Reach level 5 in multiplayer and complete waves 1 through 10 on the War Machine map in Horde (any difficulty).
• "Ride It All Night Long" (10 points): Reach level 10 in multiplayer and complete waves 1 through 10 on the Highway map in Horde (any difficulty).
• "No, But His Face Rings a Bell" (15 points): Reach level 15 in multiplayer and complete waves 1 through 20 on the Sanctuary map in Horde (any difficulty).
• "Lost in Transition" (20 points): Reach level 20 in multiplayer and complete waves 1 through 20 on the Way Station map in Horde (any difficulty).
• "Like Father, Like Gun" (30 points): Reach level 30 in multiplayer and complete waves 1 through 30 on the Allfathers Garden map in Horde (any difficulty).
• "Am I Only Dreaming?" (40 points): Reach level 40 in multiplayer and complete waves 1 through 40 on the Memorial map in Horde (any difficulty).
• "Blood on the Sand" (50 points): Reach level 50 in multiplayer and complete waves 1 through 50 on the Nowhere map in Horde (any difficulty).
• "Afraid of the Dark" (20 points): Play a multiplayer match on each of the seven Dark Corners Map Pack maps (any mode).
• "Did Not Go Gentle" (30 points): Win a multiplayer match on each of the seven Dark Corners Map Pack maps (any mode)
• "Is it Hot or Is That Just You?" (25 points): Kill 25 Bloodmounts with a Scorcher Flamethrower while playing Horde on a Dark Corners Map Pack map (any difficulty).
  

• A player could copy game progression data from one profile to another.
• A team could use the 50-point revive bonus to artificially increase its score in Horde. Going down but not out (DBNO) in Horde now subtracts 50 points, so there is no advantage to using the revive-bonus technique.
• A player could get 2 points for each kill in Wingman.
• A player could continue to shoot the Flamethrower while performing special movements like evading and mantling.
• A player could cause heavy weapons to spawn continuously while playing Horde.

• An issue that could cause players to lose all achievement progression if they signed in during a loading screen.
• Issues related to the Smoke Grenade causing a player to cringe instead of knocking them down. If hit by a Smoke Grenade with cringing turned on, players will now:
• Drop the Boomshield, even if aiming while carrying it.
• Drop a heavy weapon, even if it is deployed.
• Cringe while roadie running.
• Cringe while in cover.
• An issue that prevented players from shooting around the lower left side of a planted shield.
• An issue that could cause a DBNO player to not appear as DBNO.
• An issue that prevented Gears players from inviting players of other games to join them in progress in a Private match using DLC.
• Issues that caused rich presence information to become inaccurate.
• An issue that caused the overall achievements progress bar to not reflect the latest achievements.
• An assortment of localization bug fixes.
• Additional miscellaneous bug fixes.

• Adds a 30-second delay in map-based weapon spawning at the beginning of a Wingman match.
• Adds more future server-side balancing options.

• Giant gameplay: Gears of War 2 played on Giants Stadium LED wall
• Spot the cheater: branded Gamercards to be handed out by Microsoft to cheaters

Via Epic Games forums