It is vary rare for a game to make me want to willingly stay up all night, so that's my endorsement. I went in knowing nothing after finishing Chaos;Head Noah (not required to play this but there are references to it) and I can't recommend it enough. The story, art and music is excellent and well worth your time.

Most of you probably already know this considering the popularity of it's anime so instead of going over that well trotted ground I'll mention the fan patch by Committee of Zero. It has a lot of features like an updated translation, bug fixes and additional subtitles, but the best improvement is switching the phone font for something more readable. I can't imagine playing this without it. The page says you can toggle what features are enabled though I can't vouch for that as I played it with all the improvements.

Also it adds back the cosplay patch if that's your sort of thing.

playing Steins;Gate in your 10s vs 20s is a completely different experience

The best time travel story you will ever experience. Read it.