If you want to work in the gaming industry as an artist, you should first answer two questions: 

1.What exactly do you want to create? Characters, weapons, transportation, environment?
These spheres sometimes overlap, but you should still choose something particular for a jump start, as it determines the knowledge and pipelines you’ll need to master.

2. In what style do you want to work? 
Indeed, the style has much in common with realism; these are not two distinct areas, and at some point, you can transfer from one to another. But when it comes to your portfolio, you should determine what you’ll show to a prospective employer. 

Do you want to work on Overwatch-style products? Then look for references and concepts of artists who worked on them. Shape your portfolio in this style. 

Don’t spread yourself too thin. Show exactly what the employer needs. Do you have works in different styles on ArtStation, and you are not sure what to choose? No problem; just determine the style that your particular studio employer needs, and send them the best you have in that selected setting. 

Know the difference between a portfolio and a gallery of works. The former is needed to engage the client, while the latter showcases all your interesting projects. Differentiate the two and don’t mix them. 

Your primary competitors are people already working in the industry. Based on this, your works should comply with expected quality standards. At first, you might fail to create something up to par with the studio level, so don’t be afraid to go back and remake your first works. 

If you don’t want to remake and refresh your weakest projects, then remove them from the portfolio; they may spoil the employer’s impression of you. 
The chain is no stronger than its weakest link.

Don’t be shy to show your works in expert groups, chats, on forums, and on ArtStation. Even if you think the work isn’t ideal, be open to constructive feedback from colleagues and fellow artists. Besides, if you hide your art, how will a potential employer find you?