Immersion. Suspension of belief that I'm part of a game's living world. The qualities, or attributes, that any specific game has vary greatly, and what we, as individual gamers look for also varies. The "attributes" of a game that creates immersion for me may be despised by others, which is fine, while what others look for can be a negative for me.
I tend to be a bit "old school" with regards in what I look for a game, because, well, I am old. It's not that I mind innovation and progression in how games are developed, which is inevitable, but sometimes those "innovations" aren't that great to me, or end up "dumbing down" the players involvement within the game. I often see games criticized in forums and in the press (no offense intended PCG) for bringing nothing new, or using the "same old formula" for creating their game.
Bethesda and
Piranha Bytes are studios that are often criticized in that manner, and I personally, respect them for sticking with their basic formula in game creation, because I have that immersion.
So what creates that immersion for me? The following are some of the gaming "attributes" that I look for when buying a game. Listed in no particular order, and no one game encompasses them all, and some games may only have one or two. But these are qualities that create immersion for me within a game, and immersion = fun.
Character Creation -
@ZedClampet did a post about how long you were willing to spend in character creation. It's a negative to some, but I've spent literally hours in creating a character, especially in AD&D games. I'll tweak, and roll dice, debating over how to spend points on attributes, skills, abilities, ect. Or choosing character history/background, anything that help define my character, or group of characters to be able to handle all situations.
Story - Is a primary concern, how well it's written, my character's or party's involvement in how it evolves.
Companions and their personalities/back stories - huge for me when it applies to a game, as not all games have them, but when they do, they should feel real. Emotions.
NPCs - characters that play an important role, though not companions. Varies widely, but if they have a personality, an effect on the story in how you react with them it's a plus. So is a day/night schedule, rather than just standing around in the same place, saying the same lines over and over.
Exploration & Discovery - perhaps the most important irregardless of the games perspective (1st or 3rd person or isometric) and whether the game is open world or map based.
Combat Mechanics - I've played real-time, real-time w/pause, and turn-based. The implementation of a combat mechanic can make a game, or make it a slog.
Weather Effects/Day-Night Cycle - not all games have them, but when they do it can really increase immersion for me.
Crafting - I love a good crafting system, whether is weapons, armor, alchemy, or food. I can spend hours in a good, detailed crafting system. I include in this settlement or home base construction like in Fallout 4.
Inventory Management - I love it, and I know many gamers who outright hate it. That's cool, we each have our own "thing". Whether it's based on weight (which I prefer), or inventory size limits, or something else, I love that micro-management.
Survival Mechanics- Not all games have those, though many can be modded in, but the best survival mode that I've experienced in a base game was in Fallout New Vegas. Eat, hydrate, sleep, and dealing with diseases.
Modding Community - Varies greatly by game, but being able to mod a game (even in the future) to my specifications is a huge plus.
End Game - It's more than just a "boss battle" to me, and more how it ties up everything your character has done or said throughout the game. Everything your character(s) has learned and experienced should play a part. There's a lot of variables here, so I won't go into detail as other posts have done this.
So, anyway, those are some of the main things I look for in a game for immersion and fun.