In short, it's totally worth watching!
ReLIFE is one of those hidden gems of anime. The concept is something new; it is one of those breath-of-fresh-air anime that you don't feel like stopping watching. To be honest, the age thingy took me by surprise. I started it with a SoF rom-com in mind, but boy, was I amazed? It's definitely worth a watch, whether you are a fan of Rom-com as a genre or not.
The plot is immersive, without much cliched stuff, and the characters are just awesome; you won't feel bored even for a moment.
Apart from these, this anime also helps both teenagers and adults to realise the true value of the moment they are living in, because it's something that won't come back.