The hardest part would be the functions/controls.
The most fun--why the title, of course!!! I love making up my titles and realize they might not all make sense for you guys, but they do to me. I get a bit bummed when it is just hum drum.
BONUS--When I can add a helpful picture or two; ones that actually do help the reader decide on the product!!
Oh!! Bigger bonus--When someone tells me they got the item based on my review and they love it as well!!!