Renamed meteorslides_featured_image_array() to meteorslides_add_featured_image_functionality_for_slides(), since that is what the comment says it does. Removed comment.
Same kind of change for meteorslides_featured_image() -> meteorslides_add_featured_image_sizes_for_slides
Created a meteorslides_get_options() to remove the duplication of calls to get_option( meteorslides_options ).
Named a parameter in call to add_image_size() for readability.
Refactored the CSS and JS enqueueing code to use "stepwise refinement" and speak english.