Concept art shows the ideas people have for a game such as layouts of buildings or character designs, these will usually be based off of some descriptions given to the artist, once the design is finished changes can be made accordingly.
Examples:
The Call of Duty: Infinite Warfare concept art shown below is a first look at the main hub area of the campaign, as you can see it is not fully polished as it is just for demonstration but it shows enough to link it with the final design. For the design brief the artist was tasked with creating "an inter-orbital aircraft carrier that would function as a fully interactive player hub experience". This artwork and more can be found at http://conceptartworld.com/news/call-duty-infinite-warfare-concept-art-mike-hill/
Overwatch has many diverse characters that fit into its somewhat cartoon-like world which uses a cell shaded art style , some of which went through some very big changes during their concept art phase. One of these was the decision to split one character into two siblings, The original design for Genji had him use both a sword and a bow but due to how different his two weapons were and how they might affect gameplay, he was split into the newer Genji, still wearing the original helmet and using a sword and shurikens, and his brother Hanzo who took the bow from the original design.
Another set of major changes was to Pharah who went through different colour schemes, body types and even different genders. She was always depicted using a rocket launcher and being able to fly so the changes were to the character herself instead of anything gameplay related. As shown below the changes to her character were very obvious, she has had possibly one of the most different incarnations in the cast of characters
There were a quite a few stages of D.Va's design however most of the changes were to her mech as D.Va herself reached her final design in stage 3 whereas the mech took 5 stages to reach its final design. The early concept art shows the mech to look more humanoid than the final design which is designed to look similar to a rabbit.
The final designs for most of the Overwatch cast can be found at https://playoverwatch.com/en-us/media/
Below is some concept art for Sonic the Hedgehog, as you can see from this Sonic was originally a very cartoony looking rabbit, he then made the transition into a hedgehog, the first hedgehog design featured more sharp looking edges and an angry look on his face, at this point in time his name was Mr Needlemouse but as time progressed Sonic gained a more rounded look with less spines on his back and a slightly less serious face as he was being marketed to an american audience and this was more appealing to a wider age group as to attract a bigger audience, it was also at this time he was given the name Sonic.
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| Source: http://www.sonicretro.org/2016/06/never-before-seen-concept-art/ |
Below is concept art for Mega Blaziken from the Pokemon games, the concept art shows different aspects of the final design such as the feathers on the back of its head which give it a more streamlined appearance which fits the theme of speed which is a common trait of this Pokemon. at the edges of the picture you can see concept art of the individual limbs to get a better view of smaller details.There are also samples of patterns and colour schemes to the side.
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| https://pbs.twimg.com/media/B_TbNczXAAARYar.png |
