I only have 1 game maxed on my PS3 (Dynasty Warriors 7) and only 2 more games I am actually trying to max (Deus Ex Human Revolution, Warriors Orochi 3).
On 360 i've got a few games maxed - I don't count a 360 game as maxed unless dlc is maxed as well as base game since it adds to the total gamer score. The ones I am proudest of are:
Warriors Orochi 2 (the hardest part of this was unlocking the last dream mode level needed for an achievement. Had to grind grind grind)
Skyrim (base game achieves were easy, dlc was a pain)
Fallout New Vegas (Lonesome Road was a pain. Also I had to play through Dead Money twice cos I forgot to save near the end. That was annoying. Love the game but the dlc is mostly a pain)
Mass Effect 3 (Insanity for the most part was easy but I got stuck in a few really silly places. Like, the bits you expect to blitz through I spent days on and the bits I expected to struggle with were easy)
It depends on the game for me. When I get a game, the first thing I do after loading the game is have a quick look through the achievement list. Just to get an idea. I don't look at the descriptions and if any are secret, I don't look them up online. Then after 1 playthrough I decide if i'm going to try to max it or not by looking at the secret achievements if there is any left.
If I know a game is do-able, I will max it. (for example, if it's all story achievements like Oblivion)
If I think a game is do-able with a bit of effort, I will try to max it. (for example, Fallout New Vegas. Not all are story related, some of them you have to go out of your way for but it's nothing too insane except maybe Hardcore mode or the food one haha.)
If I know I can't max a game for whatever reason, I will still play it but I won't attempt to max it. (For example, Call of Duty has achievements for Zombie mode. I hate zombie mode so I will never be able to max any of those games)
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Currently obsessed with: Mass Effect, Dragon Age, FC Bayern München and Kuroko no Basuke.