Not really certain why, but Valhalla Knights is currently free on the Playstation Store and that without the need for a Playstation Plus subscription. Please note that this is only the case for the US store, so be sure you redeem it with the proper account.
If you enjoy versatile roleplaying games with tons of customization, then this might be up your alley. It features active battles, played on a separate field, between a group of characters, though it’s also possible to halt time to cast spells and such. There’s also a multiplayer component, if you’re into that sort of thing.
This game is playable on both PSP and PS Vita and comes in at a 601MB download. You can get Valhalla Knights free here.