Estimated achievement difficulty: 5/10
Offline: 50 
Approximate time: 40-80hrs (depends on side quests)
Minimum number of play-throughs needed: 1 (Start on hard)
Missable achievements: Yes
Does difficulty affect Achievements?: Yes
Unobtainable/glitched achievements?: No
Kingdoms of Amalur: Reckoning is a story guided by author R.A. Salvatore. You play as a "fateless one," guiding yourself on a journey through the Faelands to fight Tirnoch and and his army of Tuatha. You will upgrade skills and abilities to help you fight, craft, pick, and stealth your way through a cavalcade of creatures and quests, in this very open-ended game.
Preparation/Playthrough (Hard difficulty):
This game offers a very straightforward achievement list with all very easy, but time consuming achievements. A grind for achievements will be slightly more taxing than if you were to play through the game normally but still just as easy.
Six of the achievements are strictly unmissable. Read through the guide for all the others but know that about half will come while trying to do the faction achievements and crafting except for: Out of Your League, A Wink and a Smile, and Destiny Dominated. All of these can be easily obtained by following the descriptions under their respective achievements. All the other achievements that seem missable in the normal course of play can be obtained easily after the main story has been completed.
The most time consuming achievement will be "Loremaster" as it will require you to explore much of the world on foot. Keep the maps of Lorestone locations handy, found HERE, and you should be able to knock this out efficiently. Use this list of trainers to maximize your skill points to save time and use skill points from leveling toward other skills.
Make sure you start your game on Hard and do not change the difficulty at any time to properly unlock "Destiny Dominated."
In order to get achievements for each skill-based achievement (see trainer list above), you'll need the minimum rank in each skill:
Alchemy - 5 points, 3-5 should be sufficient until you find the 4-6 trainer.
Blacksmithing - 10 points, buy as much training for this skill as possible - the first trainer is at the warsworn camp.
Detect Hidden - 2 points, if you max detect hidden it will make finding lorestones much easier.
Dispelling - None, 4 points will make this much easier.
Lockpick - None, 2-3 should suffice just for getting you the achievement.
Mercantile - None, less points will actually net you the spending achievement faster but hurt your gold income.
Persuasion - None, best to wait to get to House of Ballads and purchase training from Ellova after the tutorial.
Sagecraft - 8 points, again save for training, buy when you can spare it.
Stealth - None, 3 points will get you enough to get the backstabs.