-Estimated achievement difficulty: 7/10
-Offline: 60 (1225)
-Online: 19 (525)
-Approximate amount of time to 1750: 100-125 hours (60-80 for 1000)
-Minimum number of playthroughs needed: 2
-Number of missable achievements: None
-Glitched achievements: None
-Do cheat codes disable achievements?: No Cheats
Gears of War 2 is nothing like the time sink that Gears 1 turned out to be. There are still a few achievements that will require some grinding, but they are quite easier this time around. Now, I estimate 60-80 hours, but it may go much faster depending on how you do things. Getting Seriously 2.0 can take as little as 18 hours if you do nothing but Brumak your ass off, then you will need two plays of the campaign at 6-10 hours each and then all the public match achievements could take a very long time if you don't have a good team and get unlucky matches with crappy randoms. So, this time will vary depending on your skill level.
Step 1: Co-Op Campaign + Collectibles
Grab a collectible guide and a friend, then start your campaign on any difficulty (Insane will not be available yet). Obviously Casual will go the quickest, but I did mine on Hardcore for a challenge. After this you will have all the campaign achievements, co-op achievements and collectible achievements.
Step 2: Insane Difficulty
Remember that friend you had? See if you can grab him again. Either go through together on Insane, or have your friend be on Casual which will allow him to lead you Rambo-style through the game extremely fast.
Step 3: Local Matches
All of the achievements that say "(any mode)" on the end of them can be done through Local matches against bots or another "human" player which will just be a dead controller than you move when necessary. Go through all the weapon achievements/executions/etc. using this method.
Step 4: Public Matches + Horde Mode
Now here is the first real challenge. You will want a full group of friends or people from the forums looking for these achievements, as communication is key. You might get lucky and win every single match or get every single capture, but chances are you're looking at a few days worth of playing for these.
Step 5: Seriously 2.0 + Party Like it's 1999
Now you need to grind out the two longest achievements in the game. Use the Brumak method mentioned in the guide below to finish off Seriously 2.0 (which as I mentioned can be done no faster than 18 hours, more like 22) and then leave your game running while you're asleep or at school/work for the 1999 rounds played.
If you are looking for a group to boost with, head on over to the Achievement Trading Thread to find partners to play with for the horde and other multiplayer related achievements.
There are 5 DLCs available for Gears of War 2. Getting through all of the DLC will take you quite a bit of time and a lot of grinding through for the Horde and getting to Rank 100.
Combustible Map Pack
You can get The Roof! The Roof! The Roof!... and Forged In The Fire by playing locally with two controllers. Start a local multiplayer game with your second controller as your opponent with a 1 kill limit, and kill them on the relevant map. Trial By, and On, Fire can be done alone, but as with all horde games, it is easier as a team. Use the Achievement Trading Thread to find some allies. The only achievement from this DLC you will need to play online for is Annex: Now With Execution Rules. These are public matches, so you can still play with your friends.
Flashback Map Pack
You can do all of these on your own if you like, but the horde mode achievement (Skeletons in your Closet) will be easier with a group. You need to get to stage 10 on all 5 of the Flashback maps, which may pose more problems than the three from the Combustible pack. More Mystery, Less History can be done locally with two controllers. Again, this is done by putting your other controller on the other team and killing them once on the relevant map. Bound by a Shared Past requires you to win in the Wingman game type. It is pretty simple to win against casual bots, but you can add extra controllers to make life easier if you need to.
Game Title Update
This DLC introduced the ranking mode for online mutiplayer. The achievements are for reaching ranks 5, 15 and 25, and you will get these while going for other achievements. You will need a total of 82884 XP to get to level 25, and XP is gained on any multiplayer game type.
Snowblind Map Pack
Frigid Body Dynamics and The Weather Outside is Lethal can be done locally with two controllers using the same method as in the Combustible and Flashback packs. You will benefit from finding friends to do the horde mode achievements to get Icy Dead People and Never Eat Red Snow. You will need to reach level 50 and 100 respectively to unlock Battle Hardened Gear and Veteran Gear. If you get to the relative levels, you can again use the 2 controller method. However it is more than likely you will have played these while trying to get your wings.
Dark Corners Map Pack
This DLC also contains an extra level, a deleted scene called Road to Ruin. You will need to run through this twice, one using stealth and again going guns blazing to unlock My Way or the Highway and Highway to Hell. Doing this in co-op will get you Two for the Road. You can get Afraid of the Dark and Did Not Go Gentle locally with two controllers. The rest of the achievements need you to get to certain waves of maps on Horde while being at a certain rank. You will want your wingmen for these!
Gears of War 2 is a long old slog to 1000 and even longer to get the full 1750. It is rightly so one of the most popular games to grace the Xbox, so there are not too many games worthy of having so many hours pumped into them. Happy killing...
[x360a would like to thank The Pants Party for this road map]
[x360a would like to thank Corrupt x360a for the DLC additions]