*Aldnoah.Zero - mecha/sci-fi
*Gundam Iron-Blooded Orphans - mecha/sci-fi
*Gundam Unicorn - mecha/sci-fi (and you don't need to watch all of Gundam to understand it)
*Black Lagoon - Very action packed, guns blazing
*Jormungand - Also guns blazing anime about arms dealers and a child soldier
*Fandyllic already said this one but Psycho Pass is very, very, VERY, good sci-fi if you haven't seen it already.
*Phantom: Requiem for the Phantom - Japanese nationals become mafia assassins
*Noir - Two female assassins take on entire mafias, starts off slow but gets more action packed as the show goes on
And if you're interested into some really good sci-fi that isn't anime and have Amazon Prime, try The Expanse. Amazing sci-fi/space show and the attention to detail in it is on godly levels.