First let me say that this is an excellent plugin! Especially so when you're building a website for clients or friends who don't really know how to resize pictures before uploading.
I do have one feature request though: add an option to specify the image quality after resizing, e.g. 60% for JPEG pictures should be good enough.
I noticed that when it resizes the image to 1024x1024 pixels (default WordPress "large" image dimension), the image size is slightly more than 1MB. This is for just a normal picture taken using a digital camera. Surely at 60% JPEG quality it can go down to 100KB - 200KB in size.
That should make it much faster for the user to upload the image, and much faster for visitors to download the image, with barely any noticeable difference in image quality.