There's quite a lot to Acheev, read more about how it works - and particularly Acheev's Green/Blue completion features for 100% completion of games, even when there are Unobtainable achievements.
We welcome input to our guides; both as suggestions/corrections for improvements (for anyone), or go for Editor status and write your own guides! Any and all contributions are welcome - but please read our guidelines on contributing achievement guides as well as the achievement tagging definitions.
We're hard at work with an awesome vision for Acheev. New site updates are posted frequently, with changes noted in the the changelog here. Please also see the Roadmap for planned features coming soon, and also Known issues for any errata.