Though I haven't tried this yet (Looking forward to it when I have the time), I wanted to leave my own 2 cents about the achievements thing.
I think it could be a pretty good & worthwhile idea, but only if there's rewards that you can unlock in-game. It could be anything from a different aesthetic for the suits/guns (So it doesn't cause balancing issues by making stuff overpowered, stat boosts could cause dominant strategy), to extras like an art gallery or even commentaries. It means it could be worth the player's time, instead of just being for bragging rights. There would even be the chance of more people being interested in going for the extra challenges.
Any other ideas I'd have right now would only tie to what I'm suggesting, so it's an uncertain basis to go by. Think I'll just leave it this, and if the idea interests you, I could go into further possibilities if it's going to be of any use to you.