 If you liked
Shinseiki Evangelion
|
 ...then you might like
Suisei no Gargantia
|
Both revolve around weaponized mechs, have heavy psychological themes that address questions like how to define humanity, and feature a large plot arc about the main character who was derived of choice learning how to think for himself.
Evangelion is much darker than Gargantia; Gargantia has a much lighter/brighter art style with weaker characters, but if you liked Gargantia for its psycholical themes and mech fighting sequences you'll like Evangelion a whole lot more. Give it a shot.