Life is Strange is truly a great game. But yes, watching walkthroughs pretty much spoils the whole game already, as it's based on your connection with all characters in the game.
This is what makes the tissues a necessity as I can't really imagine the game being as moving when watching from the outside.
Guaranteed one of the top 10 games of the decade 10/10 would recommend.
It is not only interesting as you play but it gives you a lot to think about, I could even claim you would learn a lot form it too.
The choices do really matter too as from this episode on I really can find back a lot of differences between my game and my friend's games.
That's also why I didn't need the tissues, because I took the lame and boring options... No regrets on that though.
One last recommendation, go in completely blind, try to find your way in the game alone, don't go on the internet, don't read comments on anything related to this game and don't google it.