As the title says: What makes a game look good? Not, What makes a game good, But how do you make the game look good?
Come with answers!
Things that can make your game look good: Particle system, (Dust particles in the air)
Understanding a game and having the aesthetic match it.
Art direction.
How long is a string?
Some young grasshopper asked :
“What makes a game look good?”
Two words.
LENS FLARES !!
YOU CAN NEVER HAVE ENOUGH LENS FLARES !!!
If in doubt, LENS FLARES !
(“My God, it’s full of stars!”)
BTW… there were threads like this if you just search the forum:
http://forum.unity3d.com/threads/113202-How-do-YOU-make-your-game-look-good
That does look quite nice…
Not sure as it depends on what you want to do, but attention to detail helps, having color harmony and why not try a bit of the golden ratio for proportions. Maybe using reference art from cgtalk. Also, adding things that are in motion can make your game look more alive, which translates to “looking good” I guess.
Oh and lens flares. If you want it to be realistic, bias your color tone almost 100% to a single color. Bloom, DOF, motion blur, and with BF3… the new thing, fake BOKEH!
A User Interface GUI Style and ArtWork that matches the games genre and age rating. For Example: Mario - Childish game with funny and cool looking Art and user interface and user friendly, or Call of Duty - bloody, mature 17+, with slick and military like artwork and gui with lots of things to worry about (non user friendly for noobies). Would these two games look Awesome if you revert all. Mario all bloody with guns and complex ais with adult words, and CoD be like happy with rainbows and sunshine and happy music while multiplayer swarms with frog like players jumping across building like its zero g. It wouldnt look cool, now would it - combine ArtWork and GUI, Music, and for what age it is meant for and - tada, a good looking game
You know, I once sarcastically made a pretty epic lens flare picture with some surreal sentence and massive light shafts and motion blur everywhere… Theres nothing scarier than having something like that well received… Had no clue what to say to them.
Lightmapping good lighting in general.
All you have to do is juice your game up.
EDIT: They go overboard at the end, but you get the point.
Lightmapping
Art ~_~
Really? No way! Just kidding. Yes, art does make a game look good, but if you don’t have good gameplay, it doesn’t matter how pretty it is, it’s just eye candy.
I candy? Is that like i Robot? 
Haha, I just realized what I did. I always make mistakes like that.
Games look good by throwing money at them.
What Makes a Game look Good?
Image Post Effects that are only available for Unity3DPro, stuff like they up here said ^^^: Artwork, Textures, HighPoly Models, Shadows or Lightmapping, Motion Blur(I love It), Depth of Field, Rotoscoping, Refractions, Basically anything that Unity Free version cant do makes a game look good, and dont forget about Terrains with grass, trees, rocks, bushes, materials. Reflective Water also, and yes dont forget about Sun Flares, and Sun/Light related effects, FX Particles tooo.
Thats a long sentence there :]
I always say you can’t go wrong with some color correction. Admittedly it’s very possible to go overboard, but linear rendering + HDR tone mapping + color correction can make your games look gorgeous. It’s something that’s pretty easy to ignore, honestly it’s one of the least technically impressive and least flashy effects at first glance, but probably the most powerful and useful. Almost every AAA game uses it and it can vastly change the mood and feel of a scene.
(Some people don’t like battlefield 3’s color correction, but there’s no denying it has a very huge effect)
Semi-relevant: