I'll just skip the synopsis thing and pass directly to the important part.

Story - 9: It surely is a refreshing shoujo manga, adding some sci-fi to give it an interesting argument that makes you want to know if the characters will be able to accomplish their goals. Although they have the same typical events from a manga shoujo they're affected by the "knowing of the future" premise that is pretty cool.

Art - 8: It's good but a little bland, lacks backgrounds sometimes or just use simple ones. Still I like that some places actually exist and you can see the map with the direction of many locations.

Characters - 8: I really love to see how a group of friends actually are together instead of the girl just go behind her crush all the serie and just be with her "best friends" in a couple of occasions. Still the characters sometimes fall over and over again with the obstacle (don't have courage, depression, etc) and that a character cries almost every 5 pages can be a little annoying. Also the charaacter's development was sometimes too forced, like the main character feels always insecure until a friend tells her something "nice" (but it was always similar things all over the serie). Leaving that a side, the relationships between the characters are natural and likable.

Enjoyment - 8.5: Although is not perfect and fails in some things is very interesting to read. Also is from a decent length, instead of volumes and volumes of fillers.

-THIS MAY CONTAIN SPOILER-
In many ocassions it just got a little confused and pissed off with certain things such that "Future's Naho" was actually in love with Kakeru and viceversa even if they stopped talking each other for many days in numerous ocassions and have more bitter moments than actually romantic ones.

-END OF SPOILER-

I guess that the final message of this manga is to trust in your friends, try to find solutions with more people instead of keeping them just to yourself and that if you have the chance of doing something, you should to avoid keepng with regrets.
But all the story revolves around having regrets and maybe that's the biggest failure in the whole serie is that they don't just get over it and keep with that feeling all their life. Even if because they know what are their future's themselves regreted they try to "live to the limit", we all may be regreted about something else and we should just overcome to it and know that the life won't always be in the way we want and that we can't actually know what will happen because of our actions.
The character's don't seem to learn that, they just keep saying about sharing the problems to make them lighter, saving Kakeru, etc.

to conclude, I'll resume in here

PROS:
-Interesting premise
-Decent length
-Nice relationships between characters
-You don't get bored
-Good management of suspense
-Enjoyable comedy
-Importance of friendship and trust message

CONS:
-The character's development may be a little forced
-Confusing in some parts
-Inconsistences between the Naho & Kakeru relationship from the 'future's version.
-Needs a "You don't know the future" and "get over it" message

How I said before, this manga is interesting and engaging. If you're now an overanalyzing person and just want to break the routine from typical and cliche shoujo manga or just want to have a good time then you should check this manga or wait for the anime release!