And if not, why not! 880 Gamerscore-worth of Achievements are currently obtainable (the remaining 120 Gamerscore will be available by the end of Episode 5 of Spartan Ops). Let’s help each other out and spread the love.
Dawn - Requiem - Forerunner - Infinity - Reclaimer - Shutdown - Composer - Midnight (Total: 80 GS)
Just play through the campaign on any difficulty. If you do it on Normal or higher (like you should be doing) these achievements will stack with the difficulty-specific ones.
Wake Up John - I Need a Hero - The Legend of 117 (Total: 130 GS)
Complete the campaign on Normal, Heroic and Legendary. The quickest way is to play through on Legendary and you’ll get all three achievements.
Tip: Do this co-operatively. Many hands make light work, and as long as one player is living at all times you won’t have to worry abut being reset to the last checkpoint. You’ll also pick up the Bropocalypse achievement.
Tip: Some people are saying that this achievement is glitched for them. To improve your chances of this achievement being recognised, try to play straight through whenever possible (including the prologue chapter). If you have to quit out and return to a level, always begin at Rally Point Alpha. Sometimes your in-game Career doesn’t match up to your Waypoint record, so check both to find out which missions you need to repeat.
Lone Wolf Legend (90 GS)
This one is tricky. Learn the levels playing in co-op or on lower difficulties and then just suck it up and hope for the best. If you persevere you can make it. Play cautiously, and try to always have an EMP weapon on you to take down Elites shields, and a headshot weapon to follow-up. An overcharged plasma pistol also works great on Knights.
Skulduggery (15 GS)
Do a campaign mission with three skulls and on Heroic or harder.
Tip: Choose the easiest three skulls, Cowbell, Grunt Birthday and IWHBYD, and play Dawn. You can just run through a lot of this level. To make it even easier, play co-op and when you get to the missile firing sequence, have one player already standing by the missile ready to unjam it.
Tip: Play this co-operatively and all players will get the achievement.
Bropocalypse - Bromageddon (Total 50 GS)
Do the campaign co-op on Heroic or harder. Not a difficult achievement to get because ideally you’ll be playing through the whole game co-operatively anyway.
Contact the Domain - Terminus (60 GS)
Find all the campaign Terminals. I’ve got to say that out of the last 4 Halo games, Halo 4 has the easiest campaign collectables. Most of the Terminals are barely off the beaten track (and the levels are mostly very linear anyway) so you should stumble across them all with no real effort anyway.
If you’re stuck, Roosterteeth have a handy guide: