Astra Lost in Space
A bunch of kids go to space camp and end up far away from home due to an accident, and must go from alien planet to alien planet on an adventure home, each with different mysteries to reveal. I wish I could say more, but to do so would spoil this amazing series. I never hear anyone mention this, but the best always tend to be hidden. Its ending wraps up a little too fast in some ways, but it is fantastic.
Knights of Sidonia
A guy's grandfather dies, so he pilots the machine he inherited as a duty to save humanity from alien monstrocities chasing the few remnants of humanity across the far reaches of space. This series is slow and methodical science fiction series. To be fair, everything by the same author is pretty much like this one. There is also an anime, but I am not sure if it tells the entire story or tells the story well. The anime was on Netflix last time I checked.
Lucifer and the Biscuit Hammer
A bunch of teens are given animal companions and chosen by a cosmic princess to save the world from a space mallet that an evil wizard plans to hit the earth with to end all life. Everything I just said cannot do this amazing series justice, and all of it is fitting to the author. Mizukami Satoshi is what happens with a manga author gets hopped up on LSD and reads every single work by Arthur C Clark, so I must assume.
The world goes to chaos as people turn into monsters and kill each other, and one child turns into a monster made of iron and fire, but seems to keep his morality. The child ventures to save his fellow humans and the world from the abominations that wreak havoc. For a shorter series, this one is surprisingly great, and you have sadly probably never heard of this. You do not see much like this these days, which is truly sad.
A guy gets a psychotic monster living in his arm, and must protect himself from similar monsters that eat humans that are now drawn to his monster arm's presence. There is an anime that tells this story slightly different, it was really good. That one series that totally rips off the character Venom and the symbiotes from Marvel's Spiderman comics, and it is amazing. To be fair, Venom totally ripped off that monster arm subplot from Star Versus the Forces of Evil (I am kidding about this, but will note the similarities).