metaller, you seen Legend of the Galactic Heroes? it's not new, from the late 80s thru the 90s but it's pretty universally regarded as a top of the top of the anime heap.
(if you are interested, watch this first http://anidb.net/perl-bin/animedb.pl?sh ... e&aid=1307
, it's a movie pilot, of sorts. and then the series. http://anidb.net/perl-bin/animedb.pl?show=anime&aid=584
and here's a relationship graph of the series and prequels http://anidb.net/perl-bin/animedb.pl?show=rel&aid=584
newer stuff, generally regarded as great include Mushishi
and its sequels, sort of a period piece, based around a guy who helps people deal with shinto god and yokai problems. top notch. really any series under the mono no aware tag
is recommended (except NieA Under 7? I haven't seen that).
The directed by works of Yuasa Masaaki
(from Mind Game on down), all recommended.
One Punch Man
isn't necessarily "mature". But it's a ridiculous and over-the-top satire of typical anime with better than movie quality animation. and it's pretty funny.
I'll echo Onderhond's crazy comedy recs (Kill La Kill is a satire on anime culture and on the japanese education system a la Battle Royale, revolving around a fashion/fascist wordplay, Panty and Stocking is almost Verhoevenian satire as the thing satirized of the perversity of anime culture. they get naked and fuck around a lot but also solve angel/demon crime cases, kind of cocaine + meth + Scooby Doo) + Space Patrol Luluco
, a very brief series (13x8min). By the same company that did Kill La Kill, Trigger.
(The works of Trigger et.al. started with Tengen Toppa Gurren Lagann
, a series about two boys, one younger, one nearing adulthood, living in a post-apocalyptic society where they've been forced underground who break thru to the surface after a giant mecha crashes thru their ceiling. the mecha is piloted by an anthropomorphized creature, a species who start out as the bad guys. the bombastic mecha fights are the immediate focus but ultimately the relationship aspect is key. the series is pretty wonderfully structured, narratively and literally, around spirals and it just keeps spiraling, especially in terms of scale... again, not exactly what you're after, but still, a notable, influential, acclaimed series from ~10 years ago).
Personal favorite of mine is Bakemonogatari
and its sequels (very essential to keep watching) even if, at first glance, it doesn't seem like the thing you're after. it is about a highschooler but it's much more literary, psychological, and certainly meta, than your average series.
Sayonara Zetsubou Sensei
is an absurdist, highly stylized meta parodic comedy about a high school teacher who is "the world's most negative person". Constant wordplay and references might make this a challenging pick if you're not familiar with the language and culture (or, you don't want to read all the footnotes/endnotes/blog posts/&c. ...)
Shouwa Genroku Rakugo Shinjuu
is highly rated as well but I haven't seen it so I can't vouch for it personally.
I have some other recs, but I have to leave for a bit, so, maybe a response about which of those interests you and I might figure something else out.