Your plugin seems to fill a space better than any other competing plugin which is why I found it a tease that it falls slightly short in the following areas:
(p.s. I tested this using firefox on wordpress 3.51)
a) the setting to remove image crop editor does not actually remove it. I am using post thumbnail editor which does the job more thoroughly. Could a suggestion be to either leave this to another plugin, or at least make this functionality complete enough to match or do better than post thumbnail editor OR just fix the removal setting so it works.
b) your image crop editor, even if someone does wish to use it, doesnt seem to recognise custom image sizes. This is the reason why I want to remove it, it is little use of you cant edit all the other preset sizes created ( I am using simple image sizes plugin so all kinds of custom sizes can easily be created without even going to functions.php)
c) your image crop editor is not intuitive and easy to grasp for the layperson. E.g. you have to click and drag within the image to crop, that is great, but you have to try this by accident before you know. there is no instruction to clarify that this is what you do - not a big deal, and many would probably find out after a minute or so, but these kinds of functions need some spoon feeding for the kind of clients I have!! Also, the image sizes are not labelled e.g. says 150x150, which is good, but it should perhaps also say "Thumbnail". For alot of people the label has meaning, especially if lots of custom image sizes are created e.g. "Product image". It is not obvious to know it is the product image if all the crop editor says is "180x180" for example.
d) settings could be more granular - why can you not remove the description field if you need to. Providing a polished set of functions to clients can sometimes mean removing something so that they dont get caught up figuring out how to use a redundant field.
e) if you DO need the description field, why not give it a full blown editor (more of an enhancement, but worth mentioning) I use slideshows that make use of the description field, but it would be nice for the layperson (my clients) to be able to manage their descriptive info for each attachment with an intuitive editor - they dont know html nor do I expect them to.
f) you cannot edit the title and caption fields directly as they show in the meta box. You have to click edit first. Again, not a big deal, but it would make it better (the similar "attachments" plugin does do this) The big advantage of this is that if you have 40 attachments (for a gallery or something) you can scream though configuring all the captions quickly. If you have to click on edit 40 times, that REALLY slows this efficiency down.
I have only gone to the trouble to provide this feedback because your plugin is the closest I can find to properly filling the needs of managing attachments, and it is worth it. I find the most successful plugins are not just the ones that recognise someone has installed wordpress for themselves, but rather recognise that web designers install wordpress which they give to their clients, and want their clients to be impressed by the back end functionality and ease of use.