I have figured out that this code has "die" in it which I think is keeping my init from running.

      if(!isset($this->urlParams['Action'])) {
         if($this->SingleAlbumView()) {
            die($this->renderWith(array('ImageGalleryPage_album','Page')));
         }
      }

Ahh.. that makes sense. Yeah, something was weird there.. when i just put return $this->renderWith, it came back blank, as I remember. die() was the only thing that worked for some reason. If you figure it out, let me know, and I'll make the update.

Here is what I did to make this work.

I added: public $useTemplate = "ImageGalleryPage_album"; to ImageGalleryPage.php

and changed the ImageGalleryPage.php init to look like this:

   public function init()
   {

      parent::init();
      self::prototype2jquery();
      Requirements::css('image_gallery/css/ImageGallery.css');
      
      if ($this->useTemplate == "ImageGalleryPage_album"){
         if(!isset($this->urlParams['Action'])) {
            if($this->SingleAlbumView()) {
               die($this->renderWith(array('$this->useTemplate','Page')));
            }
         }
         else if($this->CurrentAlbum())
            $this->includeUI();
      }

   }

then I set the public $useTemplate = "ImageGalleryPage_album in my subclass, then it all seems to work.

Unfortunately, the ImageGallery is built to output uniform sized thumbnails and full-sized images. If you want to break that convention, I'd recommend using the ImageDataObjectManager to build your Image class and template.