E.W.
If you have not been to Celebration Park in Allen you must go, I know it is not half way but it is pretty awesome!
We have a great community park with a small splash pad here in McKinney off of Ridge and Eldorado near Elliott Elementary (in Frisco ISD). Ledbetter park in McKinney is nice. I heard there is a sand park near the Fairview shopping center by the Purple Cow (have never been but heard it is pretty neat). Look on City of McKinney's website they have them all listed :)