Reborn is one of those strange series, the ones that by all rights should not be very good.
Firstly, it starts with 70 chapters of directionless padding that only serves to put off the action fans who would love the rest of the series and to entice a fanbase that are probably going to leave the series after the padding is over.
Secondly, when it does become more Shonen Action-y, it has a tendancy to have the protagonist pull new powers from his arse. While this has worked for some series (Bleach) it is not a particularly good form of story-telling, especially when the fans become so disillusioned about the fights that they begin to think that the hero is invincible, removing all tension.
A third problem is that all the characters that are not the main protagonist and his party, get little to no screentime (panel time?) and really only serve to make the viewer ask why they were introduced in the first place.
However, for Everything KHR does wrong, it does ten things right. The fights are well varied with 7 different main fighters, each getting the same ammount of fighing, makes for a break-up of monotony. The fights are short, usually 2 chapters, which is a rarity amoung shonen long-runners. The plot s interesting, it is always interesting to see where the story takes its heroes next. From a fight with an escaped convict to stoping the destruction of all dimentions by travelling to the future, this series has it all.
In conclusion, if you like Shonen action, this series will not disapoint.