I visited Harlingen, TX last year as I was driving back from Mexico. It seemed to be a quaint Dutch town and while it was not a bad experience, it was lacking in attractions and unique entertainment.
As a supporter of the troops I did very much enjoy seeing the Iwo Jima Memorial. It was a pleasurable experience and it was very fascinating to see.
When looking for food in Harlingen, I highly recommend the Mexican bakeries in town. Not being from a place so near Mexico, I had never been to a Mexican bakery, but the food as unique and quite excellent to say the least. Other than the bakeries, I was disappointed with the lack of restaurants and especially quality ones.
If you do find yourself in Harlingen, South Padre Island is a short drive away. This is a gorgeous island that is perfect for anyone looking to relax. The beaches and water look like they leapt out of a magazine. It is well worth the visit and you will be sure to have quite a bit of fun while there.