Watch the (wonderful) anime instead.
Steins; Gate is 95% a visual novel. That's to say that player interaction with it is overwhelmingly limited to just clicking the mouse to move on to the next line of written dialogue. The remaining 5% of the experience might be considered as game play but only in the most simplistic terms.
Having already watched the full anime series, I can say that Steins; Gate the video game follows the narrative of the anime very closely for the vast majority of the game.
And, as was the case with the anime, both the narrative and the characters that drive the story of Steins; Gate the game forward are mostly excellent. The key difference in the video game format is to make the protagonist's mobile phone a mechanic by which future events can be influenced.
The impact of this mechanic is minor in terms of making the player feel as if they are engaging in meaningful game play. The choices made via the phone do result in minor branches to the narrative but it isn't until the final chapter of the story (i.e. the ending options) that it becomes possible to deviate significantly from the corresponding final scenes of the Steins; Gate anime source material.
In addition, the excellent English VO work in the anime isn't adapted to the game, meaning everything is spoken in Japanese and translated via subtitles. This wasn't a huge issue but I would have certainly preferred an English audio track.
Steins; Gate the game is just about worth playing if you haven't seen the anime, and if you like the idea of clicking your way through an excellent visual novel. In spite of this, I can't go as far as recommending it. If you have seen the anime you really don't get much more from the game other than exploring a few 'what if?' ending scenarios that you'll need to sink dozens of hours into a story you already know in order to reach. If you haven't seen the anime then I would strongly argue that its the best way to go for experiencing the story.
I want to emphasize that I loved the anime, and I correspondingly appreciated this game due to its strict adherence to the source material, but ultimately, in spite of the possibility for alternate outcomes, I ultimately didn't especially enjoy playing the game version.
No matter how good the story is, game play should still add something to the experience. Steins; Gate the video game does not.