Munou Na Nana is easily compared to Death Note: you have two genius characters, one who is trying to enact their murderous plot to save humanity while pretending to try to uncover their own identity, while the other plays detective and tries to confirm their suspicions of the former.
And in terms of sheer cleverness of the plots thought up by each character, they're on par with DN's Light and L. However, the same cannot be said for basically any other element of the story. Aside from looking like a generic shonen anime from 2005, Munou Na Nana's biggest weakness is its direction, particularly in the way that it portrays the clever feats of its characters.
Each time Nana or Kyoya do something really clever, we don't actually see them do it. Instead, we skip ahead in time until moments before disaster, only for Nana/Kyoya to be saved by their genius plan which they already set up off-screen. Then explain it to the camera through boring monologue. Having your setup take place *after* the payoff feels pretty unsatisfying after the third or fifth time it happens.
There are numerous plot contrivances that might drive you crazy, but personally I think they're superfluous if you treat the series as a dumb, fun mystery. Yes, all of the students seem impossibly stupid to fall for Nana's lame-ass pep talks and phony personality. Yes, Kyoya ought to have made way more progress at this point if he wasn't so conveniently blind to some obvious details. And yes, the entire premise makes absolutely no sense if you think about it for ten seconds (how are parents not freaking out when their children all go missing at these camps?)
But if you treat Munou Na Nana like the pulpy mystery-drama it is, it's seriously a blast. Just turn off your pedant brain and enjoy the clever schemes, the goofy characters, the unique super powers and their mechanics, and the ever-deepening hole Nana seems to be digging herself into. My biggest hope is that it does well enough that future seasons can get the budgets they deserve.
