... don't give up!
I started by serving it cubed at lunch (our main meal) anyway. The fact that it wasn't very sweet was remarked upon, but didn't stop anyone from eating it.
Next I blended the cubed watermelon with baker's sugar and Meyer lemon juice (my Vitamix pulverizes any white watermelon seeds), poured some of the mixture into ice pop molds, and poured the rest into my ice cream maker for watermelon sorbet. Experience from the last time I made watermelon sorbet taught me that it isn't a sorbet that you can eat right away (too soft) but that it freezes beautifully and isn't too hard to scoop or eat. I'm pretty sure it's because of the added sugar; when we make pear or peach sorbet from fruit canned in juice it is much firmer after the time in the ice cream maker and it gets very hard in the freezer.
I still had a huge bag of cubed watermelon (it was a big watermelon) so I decided to blend some of it with water, sugar, and lemon juice to make an agua fresca. I put it into a pretty Pyrex juice carafe and will serve it later.
There is still enough cubed watermelon to serve as a snack this afternoon.
Here's hoping that the second watermelon I purchased is sweet sweet sweet. Not that I mind eating watermelon in other forms, but nothing beats perfectly sweet watermelon just as it is.