Change Folder Icon in Google Drive

UPD: as Google started to block unverified scripts, the only way to use it is copy-paste the source to your script editor. And verification requires some extra effort, so I didn't do it yet.

UPD2: if you have a lot of files it will reach the execution time limit and stop; you will need to run it multiple times (you can also set up automatic timed trigger for this)

I wrote a simple script for this. You can run it from here: https://script.google.com/macros/s/AKfycbyUvNoXzBMBDE9pnHkLUltliGwjip5x09t3PeTY_1KoXO45F6iz/exec

(if it gets stopped, just run it once again, and it will continue from where it left)

It will create two files in the root of your Drive, one displays progress and is deleted after script is completed. Other is the report which lists all folders and sizes. It looks like this.

Or you can just copy and paste the code into Google Script editor and run "doGet()" function from there:

function doGet(){
  var progressFileCompletedFound = DriveApp.getRootFolder().searchFiles("title contains 'Folder Sizes Report Completed'");
  if(progressFileCompletedFound.hasNext()) {
  return ContentService.createTextOutput("Report file was already created in your Drive's root folder, exiting.");
  }
  CreateReportFile();
  DriveApp.createFile("Folder Sizes Report Completed.txt", "You may safely delete this file.");
  return ContentService.createTextOutput("Report file created in your Drive's root folder");
}

function CreateReportFile() {
  var reportContent = CreateReport();
  DriveApp.createFile('Folder Sizes Report.txt', reportContent);
}

function CreateReport(){
  var reportContent = "";
  var progressFileFound = DriveApp.getRootFolder().searchFiles("title contains 'Getting Folder Sizes,'");
  var progressFile;
  var report=[];
  if(progressFileFound.hasNext()) {
      progressFile = progressFileFound.next();
      var json = progressFile.getBlob().getDataAsString();
      try{
        report = JSON.parse(json);
      } catch(Exception) {
         DriveApp.removeFile(progressFile);
         progressFile = DriveApp.createFile("Getting Folder Sizes, 0 processed...", " ");
      }
    }
  else {
      progressFile = DriveApp.createFile("Getting Folder Sizes, 0 processed...", " ");
    }
  var f = DriveApp.getRootFolder();
  AddFolderToReport(report, f, "/", progressFile);
  DriveApp.removeFile(progressFile);
  reportContent += "TotalSize MB   FilesSize MB   Path \r\n";
  for(var i=0; i<report.length; i++)
    reportContent += Utilities.formatString("%12.2f ", (report[i].totalSize / (1024*1024))) + Utilities.formatString("%11.2f      ",(report[i].filesSize / (1024*1024))) + report[i].folderPath + "\r\n";
  return reportContent;
}

function AddFolderToReport(report, currentFolder, currentPath, progressFile){
  var report1 = [];
  for(var i=0; i<report.length; i++)
    if(report[i].folderPath == currentPath)
       return report[i].totalSize;

  var fChildren = currentFolder.getFolders();
  var totalSize = 0;
  while(fChildren.hasNext() && currentPath.length < 2000){
    var nextF = fChildren.next();
    totalSize += AddFolderToReport(report, nextF, currentPath + nextF.getName() + "/", progressFile);
  }
  var filesSize = 0;
  var files = currentFolder.getFiles();
  while(files.hasNext()){
    filesSize += files.next().getSize();
  }
  totalSize += filesSize;
  report.push({folderPath: currentPath, filesSize: filesSize, totalSize: totalSize});
  progressFile.setName("Getting Folder Sizes, " + report.length + " processed...");
  progressFile.setContent(JSON.stringify(report));
  return totalSize;
}

UPD: the script was updated so that if it runs too long and is stopped, just run it once more and it will resume from where it left, using data stored in "Getting Folder Sizes ..." file.

I faced the same problem. In the new web interface you can click the button with folder name and select the Add star item. However, for me this does not have any effect in web interface (the star is lost after page refresh) nor in Android Google Drive app, though it miraculously works in Google Drive app on iPad. Apparently Google needs some more time to make this usable...