I admire the work they do at Charles Darwin Research Station... However, it really isn't worth a visit after the passing of Lonesome George. It was part of our cruise package excursion so we didn't have a choice, but it sure was disappointing. After a fairly long walk, we arrived at the center. It felt like a small local petting zoo (except all the animals are fenced away). It should take no longer than 15-30 minutes for a visit. Most of our tour group left immediately after the tour guide finished talking to go back to Puerto Ayora to shop rather than linger around because there really wasn't much to see.
If you are hoping to see the giant tortoise up close, then I would recommend going to the Primicia Ranch (on the same island) instead where wild tortoises roam freely and you can get a closer look (and photo-op) with these amazing animals!