Some display the image well, while others are too small,
In your media settings (Dashboard > Settings > Media), you have set your maximum thumbnail dimensions to 185 x 185 pixels. This means that your thumbnails will be cropped to fit inside a 185 x 185 pixel square container. However, this is not an exact crop, so your images will be re-sized to fit inside the container with respect to their original proportions. Since your original images are not all the same size, this is why some of them appear smaller.
For best results, it's recommended that you crop your images to the exact proportions you'd like them to be, prior to uploading. So, if you'd like all of your gallery images to fit uniformly inside a 185 x 185px square, make sure your images are square-shaped before you upload them.
If resizing your images before uploading is not an option, you can try rearranging them inside the gallery so that images with similar widths/heights are next to each other.
You'll notice that some of the don't show up at all
I got a 404 File Not Found error when I tried to click on the last image in the first row (the "Purell ATM" image). Could you try re-uploading it and then re-adding it to the gallery? Let me know if that works. The rest of your images appear to be displaying fine.
Please let us know if you have any other questions.