As is analysis by Anna Shvetz: OSU Reddit

Visibility of System Status

It is fairly easy to recognize what page you are on and where links take you. 

Match between System and real world
Most of the content is user-generated, so most of it matches the real world. There are reddit-specific terms (upvote, subreddit) but they are not technical. 

User control and freedom

It may be hard to find exactly what you are looking for. There are many tabs and also a search tool that should help, but it is hard to know exactly where to start.

Consistency and standards
Same structure and conventions are kept to throughout the site. Subreddit moderators have some control over visual elements (e.g. r/osu has buckeye leafs instead of arrows for upvotes and downvotes and a scarlet header with Brutus Buckeye).

Error prevention

Reddit has errors but not a lot of them.

Recognition rather than recall

The Help and FAQ sections are at the bottom of each page.

Flexibility and efficiency of use

Allows users to search for specific topics or filter the posts basd on what is currently trending.

Aesthetic and minimalistic design

The design if this site is busy and somewhat distracting. There seem to be extra patterns and symbols that may distract the user and take away from the aesthetic appeal. There aren't too many colors used which is good.

Recognize, diagnose, and recover from errors

The numbered errors (e.g. 502, 504) are just plain text and do not explain what the error is. When the site is overloaded, however, the error message is in plain language and accompanied by a funny illustration.

Help and documentation

There are frequently asked questions and a contact information page, which is helpful.