First and foremost: No grind. Just... Just no. I give up after 2 minutes of doing something repetitive. Any game which avoids grind is automatically worth at least trying. After this the points are pretty flexable. If it doesnt/does fit into a category, it doesnt
necessarily make it awesome/terrable.
Games with skill-based gameplay. I just dont get any joy in gaining a level in anything. Nor do I enjoy telling my character what to do and having them do the rest. It seems pointless. I would rather feel like im "doing" something in the game, and that my skill is contributing more than my characters "skill". (Cannot bear dice/random gameplay).
Book-Games. A good story is fine, but for me most RPG's (even the classic ones eg Baldur's Gate), it feels like reading a good book for 2 pages, than being forced to do some boring stuff (kill stuff, get stuff, dull combat etc) to earn the right to read another 2 pages. I always thought some of these RPG's would just be better as books. Also, I want to use my imagination a bit, so if I come accross some dead guys, and weapons in a crypt, for example, its more fun to "think up" what happened rather than have your character announce exactly what happened.
Game mechanics that are less transparent: Some games hide your actual health (im forced to admit... COD) which is much nicer than being to measure the exact "healthyness" of my character. DF gives a body-part system which does much the same, only gives me a general idea. I would rather get a "feel" for these things (skills as well etc) instead of having an exact readout of the integer representing this, and some other integers representing probability etc. Basically anything I can't simply apply statistics to (statistics is boring). This gives the game a "natural" feel, while avoiding being hellbent on realism and without having to necessarily go for some super-complex mechanic. (I would like to know my character is "injured" rather than 42% health remaining, or that I am "good" at picking locks rather than "lock picking at 25/45 (700 xp to go!)").
Unrealism. If I was interested in realism I would just play RL, but I dont because its boring (too grindy). I play games for every reason that makes them not like real life. Realism? Overrated.
little "hidden things". Odd guns, unusual "logs", easter eggs. These thigns are always such a joy to find for some reason. Someone also metioned "junk files", which is also awesome as I usually end up browsing through the game directory.
Tweakability. The more moddable, the better (but it doesnt
have to be fully moddable, but its a plus).
I like to change my character mid game. I dont care is spontaneously changing race makes no sence. I always started, say, Oblivion and about 2 hours in wanted to alter my character.
Reasonable length. Games that entertain from the get-go. I dont want to (nor have time to) game for some ridiculous amount of time until the "true game" starts. Portal was great here. *Stares at basically all MMO's in existance*
Curiousity. Something that makes me *want* to play to see what happened/what can happen. Or something that lets me experement. Minecraft's red stone for example, or Powder Toy.
Lastly, "bizarre" things (partially related to above). Even entire games. Especially entire games. Anything that makes me go
. Special mention to the PS1 game "LSD", as it had me running around going WTF?!?! the whole time. I turned around a corner, and a giant toy-bear started chasing me. The hell??? Awesome. Portal and Portal 2's script also fit into this (although not to that extreme), with the quality voice acting made it a riot to play through.
I will probably post with more if I think about it, as there are always plenty of "shinies" in games which are fun.