Official Achievement Hunting - Easy games to get 100 % Achievements

To the Moon

Just finish the game, enjoy the good effort required.

'To the Moon' achievement is very easy. All you have to do is finish the game, the game only has 1 achievement and that's to finish the game so it's very easy. Took me around 3 hours to complete the game skipping all the dialogue.

Always sometimes monsters
A bird story
Long live the Queen
The Bridge
Deponia
Chaos on Deponia
Goodbye Deponia
Defy Gravity
Beyond Gravity
Finding Teddy
To the moon
Morphopolis
The night of the Rabbit
Oscura:Lost light
Pixel Puzzles: Japan
Soul gambler
Speed Runners

Super meat boy. (Khe-khe-khe)

grimind, just have to find some secrets

to the moon didnt give me achievement. even thou i finished twice -_____-

The Plan was quite easy.

Murdered: Soul Suspect -> steam says that i played 20 hours (i think that it was ~12h or less) to 100% but in my opinion it was really easy.

Finding Teddy and some Telltale Games as well.

eversion (they insist on writing it with a small letter for some reason) is maybe about 1 hour long with 1 more hour to replay the game and get the last 1-2 achievements.
The Walking Dead has at most 2-3 achievements that you can miss at all since all the other ones are story based.
Might & Magic: Clash of Heroes is pretty straightforward when it comes to achievements. The only ones that require any actual effort are the multiplayer ones and they shouldn't be too hard either. To put it in perspective, I recall it having a Free Weekend a few years ago before I even got the game and I got all the non-DLC non-multiplayer achievements in the span of that Free Weekend (the DLC achievements are piss easy when you have it to unlock them).
Cargo Commander's hardest achievement may as well be called "beat the game". Since it's to... well- beat the game. :P
The Baconing (and, I have no doubt, any other DeathSpank games) is straightforward and easy.
Space Run is fun, but kinda short.
Same goes for Gunpoint and Sequence... er, I mean "Before the Echo" cuz they changed the game's name.
Half-Life 2 and episodes are very easy. :D
Soul Gambler, while sketchy on exactly how 1 achievement works sometimes, is easy and short.
Intrusion 2 is awesome and everyone should totally play it... oh, and the achievements are easy.

Those are off the top of my head. Then again, I am crazy, so some of those might be slightly harder than I make them out to be. ^_^

All those Hidden Object Games. ^^

All of the games I've 100%'d have been pretty easy.

Hatoful Boyfriend, Cinders.. most any VNs.
(the Hidden Object games from Artifex Mundi, too, but I've yet to 100% any of them because I get bored halfway through. :c )
The Walking Dead, The Walking Dead: Season Two, The Wolf Among Us... Any of Telltale's games.
To The Moon and A Bird Story are super short and easy.

Make it Indie
Toren
Tengami
Forward to the Sky
The 39 Steps
Papo & Yo (Collecting the hats sucked, but I got everything else in one playthrough)
Incredipede
Journal
A Bird Story
Brothers: A Tale of Two Sons
Ironclad Tactics (There's only one achievement, and it's literally just to click the RMB at some point after you finish the short tutorial.)
Woodle Tree Adventures (Patience to collect enough berries, but it wasn't too bad)
Resident Evil 4
Ampu-Tea (arguable, but the only difficult one is made simple by serving a black coffee. Just takes a little patience.)
Whispering Willows
Oknytt (Takes all of 4 hours to finish and there's only two achievements that aren't story-related.)
Thomas Was Alone
Jolly Rover (I think you need a guide for a couple of them, but as a point and click adventure game, you can't really fuck it up. Was a lot of fun, too.)
Risk of Rain

I'm also pretty close to 100%ing Catlateral Damage, Divinity: Original Sin, Dying Light, and Resident Evil 1 HD Remaster. And I'd honestly say all of those have been relatively easy to do.
Faerie Solitaire is on there, too, I only have one egg left to find and it'll be 100%'d. But that's based on some crazy RNG and some people take like 200 hours in-game to make the last one spawn. :(

some Early Access games have very low amount of achievements at the moment (tho im guessing this will massively change over time) for example Subnautica you can get all 3 achievements within a 10 minutes

If the achievements are easy, are they truly achievements? Think about it :P

The Plan and Bird Story are the only ones that pops out of my mind. Maybe because they are the only one I've done.

Here's bunch of games I 100%ed in rather short time and that I didn't seen mentioned yet:
Alan Wake's American Nightmare (warning, don't confuse with base game, which is much longer to 100%
Bad Hotel (one achievo is SOOOO annoying to get through)
Batman Arkham Asylum (well, a bit time-consuming, my steam tells me it took around 5 days to get them all; 2 warnings: one achievo is easy to miss, and it's near the end of game; second warning: only first game has "relatively easy" achievements, as sequels have bunch of "get all medals using every character", which probably is very time consuming)
The Darkness 2 (14 hours on steam-timer; might be a problem getting coop achievos this days...)
Deux Ex Human Revolution, The Missing Link DLC, Directors Cut and Deux Ex The Fall (especially DLC and The Fall, those are rather short games)
Fallout New Vegas (easy but time consuming, most achievos are for winning quests)
FootLOL
Gunpoint
Poker Night 2 (Poker Night 1 also has easy achievoes, but they require some luck, as one of them is about getting straight flush...)
Puzzle Agent 2
Sleeping Dogs (time-consuming through)
State of Decay

The 39 Steps is impossible not to 100% since it's an audio book and you get achievements by listening to it.

Almost all hidden object games can fall into this category, especially if made by Artifex Mundi. The only to so far I encountered where it is not possible is Frankenstein: Master of Death (2 are glitched and cannot unlock, so I used SAM to add them in) and Melissa K. and the Heart of Gold (beating the Expert time on the last puzzle is impossible unless you are a Tetris the Grand Master god).

Many Daedelic point 'n' clicks have easy achievements, although many may need guides for a quick grab. The Deponia series is especially notorious for insane achievements, especially Chaos on Deponia.
Point 'n' clicks are generally easy to 100% since they only have achievements that need some out of the box thinking. And there are many short ones on Steam, like Samaritan Paradox, Shadows on the Vatican, Metal Dead…

Tengami

Tales of Maj'eyal huehuehuehue

Costume quest. It has like 3 secrets that are easy to find and all other achievements are story based. Took me 12 hours.

Absolutely EU4!!!

Dynamite Jack, maybe? I don't remember because I played it in 2012, but I have 4 hours in it and 100% achievements. It's a fun game either way.

LYNE definitely takes some effort, expect 15-25 hours for 100% depending on how good you are at puzzles. Again, it's fun either way and kind of addictive.

Every Lego game is easy but time consuming at the end

Knights of Pen & Paper +1 Edition (broken achievement & 20.4 hrs on record)
Pixel Puzzles: Japan Edition
Portal of Evil (2.9 hrs on record)
Mac Guffins Curse (13.8 hrs on record)

The Walking Dead: Season 2

By completing the campaign you earn all of the achievements

As a semi achievement hunter, I have 11 finished games, the easiest two I have are Secret Ponchos which involves owning the game and Incredipede which involves turning the achievements on.

Deponia
WRC Powerslide
The Walking Dead