-Estimated achievement difficulty: 3/10
-Offline: 23/38 720
-Online: 15/38 280
-Approximate amount of time 1000: 15-20 hours
-Minimum number of playthroughs needed: 1 playthrough
-Number of missable achievements: No
-Do cheat codes disable achievements? No
-Does difficulty affect achievements? Yes
-Glitchy achievements: No
-Unobtainable achievements: None
-Extra equipment needed: None
This is a fairly easy 1000g provided you have a good boosting group available for the online achievements. I had no problem finding a co-op partner for the runthroughs, but finding four was far trickier. Overall the game feels (and looks) like a poor man's Gears of War but once you get used to it isn't too bad.
First of all you want to find yourself a partner for the walkthrough. You have to complete the game in co-op, so you may as well get Trooper, Peacemaker, Revenant, Double Time and People Skills out of the way in one go. However, you cannot start the game on the Insane difficulty from the start. The way around this is with cheat codes. They can be entered from the main menu. Enter the word 'Revenant' to unlock Insane before you start your playthrough. Other (less useful) cheats can be found here. During this playthrough keep an eye on miscellaneous achievements, most will come naturally. The only one which may prove tricky is Dumb Luck, see achievement guide for more info. Also make sure to pick up all collectibles, use this guide to get them all. Only one of you needs to pick up the collectible and will count for both of you. Once you finish your campaign, you will have most if not all of the offline achievements and depending on lag and ability shouldn't take too long, maybe 8-10 hours.
Again make sure you have a confirmed dependable boosting group for the online achievements as there are a lot of achievements that will take time to do. It is useful to have at least one of you tracking who has what done on what map to avoid confusion and speed up things.
Overall an easy but at times frustrating 1000/1000, with an unnecessary online element to it. You should have everything done by the time you have the online element done, if not achievements carry on through different games, so start another playthrough on easy and mop up there.
[x360a would like to thank Corrupt x360a for this road map]