Lychee fruit lose some flavor if allowed to hang too long on the tree. And, the mauritius I've had so far this year were a little watered down.
However, my SweetHeart -- which gave me a grand total of 4 fruits this year -- were ridiculously delicious, just like in years past. This is the 3rd year in a row that it's borne fruit, on a tree planted in 2011 if memory serves. This year's crop would have been a lot better if hurricane Irma hadn't torn it apart. It's never given me more than a few pounds of fruit though.
If memory serves, your tree is also a SweetHeart. It's a bit odd that it hasn't fruited yet, as it had already fruited for me in the pot before it made its way to your yard, and your tree is older than mine which has borne thrice to date. It seems like there is some environmental situation that it's not fond of.
At any rate, the SweetHeart should be blissfully sweet with a hint of tart and a floral note that rounds out what is an exquisitely delicious fruit. When it starts bearing, you will understand why you waited so long.
PS -- that tree should be somewhere around 14 years old by now. It originally came from ECHO as a nice 7 gallon in 2006.