The type is datetimeconverted to the actual Javascript date in Waterline (Sails ORM). Therefore, it must be compared with a date object, not a string. You can save your code exactly as it is, but change the first line to:
var _date = new Date(moment().format('YYYY-MM-DDTHH:mm:ss.SSS') + 'Z');
Then your query should find everything Gamethat starts in the future.
Of course, since your code just returns the current date, you really don't need to moment:
var _date = new Date();
will work just as well.