Some of my favourite vita games aren't particularly hard, I can recommend:

Dragon's Crown - A side scrolling RPG which is beautiful on the vita

Playstation All Stars Battle Royale - a fun 'smash bros' like arena fighting game. All characters are from the playstation universe

Binding of Isaac: Rebirth - Just play it, it's a phenominal top down dungeon crawling adventure, where you play as Isaac, a child who uses tears to kill the monsters from below. I have 300+ hours on this... just saying, and it's cross buy!

Dragon Quest Builders - A new release coming October 11th. It's a 'minecraft' style game set in the Dragon Quest universe, you also do not need to have had any prior experience in the Dragons Quest series. You can read my blog post about it if you want.

Terraria - A side scrolling sandbox adventure game where you collect resources, kill boses, upgrade your arsenal. I also have around 200+ hours on this.

The Ratchet and Clank Trilogy: A fun story driven adventure game. You get 3 games for the price of one, an absolute bargain

Sly Cooper: Thieves in Time - another solid choice for the vita, a story driven 'cartoon like' adventure game.

Hope I helped, you can add me on PSN if you want to: DavidsonBoy_HD