Majin Tantei Nougami Neuro is on the verge of being bad imo. Half of the cases are ridiculously obvious, while the other half are deus ex machina where Neuro just randomly pulls one of his 999 spells to solve the entire case. This show lives on the comedy, and frankly it isn't particularly good in this aspect either.
Kuroshitsuji I haven't seen.
Toshokan Sensou is decent. Plot might seem to be a big thing initially, but it mostly focuses on the characters in an alternate future. It depends very much if you like the characters or not, since the story is pretty stupid.
Flag is a (very) slow drama, albeit a good one. It mainly depicts war realisitic from an individual level, rather than on a big politic level. Could get too boring at times. The realism is really the strong point of this anime, feels like you watch something with new eyes sometimes. Just that why the "Flag" could stop a whole war wasn't convincing explained, but it didn't bother me at all since the focus was on the small level.
Nijuu Mensou no Musume was decent - enjoyable but nothing special. If anything I blame the story, again. It had a promising start at least. Isn't as detective-like as I had originally expected, and many "super-powers" are indeed "super-powers" since they aren't explained.
Reqiuem for Phantom is very enjoyable imo. While logic isn't its strong point, it still evokes emotions within me. A high pace probably helps too. Personally I never had any major problems with BeeTrain animes, I've liked the characters and dark atmosphere with the awesome but overused music. Though a lot of people seem to think that the stupidness of the characters overshadow all this.
Ok let me clear afew things up for the thread starter.
Majin Tantei Nougami Neuro is like
Zero no Tuskiama except the male is the short tempered wacko while the female is innocent, she of course gets bullied by him often. Since the Demon is of course very powerful things will not spiral completely out of control, you will enjoy the anime non the less.
Kuroshitsuji is a MUST WATCH! It has the dark mood you are looking for, oh and yes there is a demon in here too. If you liked the series then go on to watch
Toward the Terra bear with me it may get slow at times but then bam! suspicious Kuroshitsuji similarities in the first arc.
Also check out
Shion no Ou for the same effect and then
Hikaru no Go for epic conspiracy. What i loved about
Hikaru no Go is that the dam Main character was leaving his Rival eating the dust FOR ONCE! I could cry happy tears and pay attention to the rest of the scenery.
Toshokan Sensou Is what happens when your government has complete control over your books and internet. Total bullshit censorship in order to control the masses, its a good watch, and if you liked the romance aspect i suggest watching lovely complex for the same hilarious height difference between the two.
Nijuu Mensou no Musume Only managed to watch one ep so far, didn't go to deep because i was afraid it was going to suffer from the same time decay like
Ghost Hound