Games that I can immerse myself in. Things that do it for me are:

• A full and developed open world that has a compelling atmosphere to it. The kind of thing where you find yourself pausing to gaze across the scenery.
• Tantalizing mechanics or systems. The kind that draws your mind to 'building' even when not playing, that will cause you to unwittingly spend hours tinkering with, and gives you mirthful glee when you put it all together and can savor its power.
• Interesting story. One with tasteful complexity, good pacing, and exciting developments. The kind of story that compels me, let alone anyone is a whole separate question of its own.
• A canvas or foundation to allow me to develop identity and investment in my character/role. Playing a specific character can also be good, if that character is compelling.
• Core gameplay mechanics or loops that are fun in and of themselves. The kind that, were the game an alpha or proof-of-concept with no "game" beyond the graphic-less, progression-less minigame, you would still find yourself enjoying your time.
• Fulfillment of a compelling fantasy. Being a FEROCIOUS DRAGON, or an UNSTOPPABLE SPACE MARINE, or an ALMIGHTY GOD, or even just a simple human living a comfy life and being able to experience the breadth and limits of that fantasy.