I started this when it first came out and followed it weekly for about 2 or 3 years, but either I got older, or my taste got better, or the manga just deteriorated, whatever the reason I stopped reading it. Recently I decided to go back and try again not its complete. Firstly, it's a lot more tolerable when a single fight doesn't take 5 weeks to get through. Secondly, I find the character interactions humorous and very interesting. That's a big plus. The back story could be better I felt.
SPOILER
It lost plausibility in its attempts to ensure that none of the heroes were truly to blame for the massacre, which stopped making sense once the egotistical emperor was revealed to have been mislead by the true big bad.
One thing that bothered me was how Sakura was initially introduced as a cool beauty with black belt level martial arts skills, and then she failed to actually use any of her training at all after about chapter 5. What was the point in her having them then?
As with every shonen this manga suffers from the typical cliches of super quick power ups, totally random training arcs, overly emotional displays of friendship and unity, lots of rather hypocritical declarations of saving people and valuing life (from a bunch of underworld assassins), and no one actually dying from their life threatening wounds.
In general though, as a shonen, I found it far more enjoyable the second time around when I wasn't forced to wait for updates. It's not the greatest mange ever written, but it's worthy of being a light read. Overall I would rate it a 5 or 6, but since it fits the target demographic well, and I'm feeling generous, I'm giving it an 8.