I think it's high time someone put's up a good review of this show. the ones that are up now are in my opinion just dead wrong. in some points they seem to have forgotten that this is anime and not real-life, so don't go overthinking why the bad guys have an army when they're trying to destroy the universe...they just have their army, live with it.
I think the story is very nicely done, sure there are things that wouldn't make sense in real life (like the bad guy talking way too much instead of just killing the good guys) but besides those obvious movie/anime scenes happening this show has some very good twists and plots. I very much liked the thriller/horror sense I sometimes got, they really set the mood for certain episodes. in other episodes they focused mostly on humour and slice of life events and yet in other about mini-robot matches make it seem like high-speed action, all sides of this anime were a lot of fun to watch and really pulled me in. it's been a few months since I've seen it so the whole 'clues business' isn't really fresh in my memory anymore accept that gathering them felt like a 'quest' in modern times setting which I think was original and fun to watch. gathering those clues also told us (and the main character) bit by bit what had happened, what the real story is.
let's not forget the giant robot though....ofcourse in real life it really wouldn't have moved but this is anime guys! don't complain about petty stuff like that (steins:gate was about time travlel and dimension transfers so a giant robot shouldn't be that hard to get over). it was fun to see them built it and at the end the whole city coming together to built it might have been a childish concept but I like it when everyone helps out to make sure the good guys win.
the animation and sound were very good in my opinion, really nothing to complain about there. in my opinion animations like these are how they should make all anime.
the characters were all very different and fun, they made sure to give everyone a real unique character with their own quirks, humour and background. it was fun to watch them all and learn about them.
all in all I really recommend watching it....don't mind those negative reviews just watch it yourself and decide what you think of it. (and if you have read them just think of one piece for example, there are so many dumb and childish things about that show but it's still awesome and everyone still watches it anyway ;)