Inzuma Eleven GO features the same characters and holds onto almost the same mood as its predecessor - but with a few key differences. Firstly, since a lot of time elapsed from when the first series ended, and since the main focus of both series is exclusively middle school soccer ligue, there was a need to introduce new characters, but at the same time keep the old ones to guide them (read this as fainservice), so on its own, a new plot developes just from that. Secondly, the mood of the prequel is slightly changed to fit the new age of middle school soccer, which in itself shouldn't be a minus to the new series. So basically, having new characters, plot and principles, at first sight Inazuma Eleven GO might seem not as great as the prequel, but it is nevertheless a relatively good watch for the more faithful fans, and very recommended for those who are curious about how the story goes on.
Maybe I'll return after the series is finished to properly review it - since my policy is to review something after having finished watching it, but I made an exception for this one because people have been saying a lot of nasty comments about the new series; how it sucks, how they wanted the sequel to be about the old characters in college or something, but I personally think that adding new characters leaves more space for newer character and killer technique design (which is actually the main selling point of the first series that was oh so popular), and also to the behind-the-scenes drama (take Tsurugi for example). So, it's not that it sucks, it's just that you guys haven't expected it and still aren't used to it. Personally, I think it's cool to see Endou as a coach (although I did root for Endou X Aki, so I'm slightly disappointed that didn't turn out).
Anyways, if you step out of the frame of the old series and look at the new series' good points, it turns out to be quite an enjoyable watch with lots of space for laughs, trolling, shipping and parody (which is what fangirls gradually enjoy in an anime, let's face it; and as for the men, well... Try it, and throw it away if you don't like it, but don't spoil it to people who are trying to enjoy it and don't ruin it to people who haven't watched it yet but just might enjoy something about it!).