This isn't REST, there are no hyperlinks and no hypermedia controls. It is designed pretty wrong. Just look at this brittle coupling!

    POST /api/player/actions
    Content-Type: application/json

    { "type": "shoot" }

How do I know what "type" of action is available to me? It isn't documented. Why should I need to know or try to look it up in the documentation in the first place, anyway? The server should just tell me what I can do, and then I act on it! Why should I need to know all these special URLs, except a single central entry point (a.k.a. bookmark)? The server should just tell me from each resource where I can go to! A more useful attempt:

    GET /
    Content-Type: text/html

    <p>The <a href="equipment#shotty">shotgun</a> is equipped.
    There is a <a href="items/157">green armor</a> ahead.</p>

    <p>You see a <a href="monsters/2018">baron of hell</a> attacking
    an <a href="monsters/1170">imp</a>.</p>

    <p>There is a <a href="doors/104">yellow-framed door</a>,
    attempt to <form action="doors/104" method="post">
    <input type="submit" value="open" /></form> it.</p>

    <form action="position" method="post">
        <input type="hidden" name="x" value="-225" />
        <input type="submit" value="move forward" /></form>,
    <form action="orientation" method="post">
        <input type="hidden" name="angle" value="90" />
        <input type="submit" value="turn left" /></form>
    …

(HTML used for ease of illustration on HN, alas JSON proper - being a dumb serialisation format - it deficient of hyperlinks or hypermedia controls, but there are extensions for it. This audience is less likely to be familiar with them.)

It really bothers me that programmers call things REST, and when you look at it it isn't REST at all because they don't know the first thing about it.