You need to go into "settings" then "graphics".  You can increase various sliders in there which will change the quality of your graphics.  Be warned, go beyond a certain point and your Frame Rates will suffer unless you have a massive CPU and equally massive RAM.

Play around with these until you get it looking how you want and then see if you can fly or if it's a slide show.

Screen resolution is important too, low level  detail looks better at high resolution than high detail at low resolution. 

Have fun.

Will

Landclass files will also help enormously.

You can get a wide variety of files from the download libraries that enhance all sorts of features from night lighting to the glass in the terminal windows. I have dozens of them LOL.

Just search for "scenery enhancements" - that should turn most of them up.