WGSP was a great day hike! If you're not sure where to go when you get there, definitely take the Gorge trail... it's absolutely beautiful! The stairs and narrows passages can really slow you down if you get there around midday (when it's typically busier), so I suggest heading out there early in the morning, but bring your coat if it is early spring or fall (after September), as it can be around 10-20 degrees colder in the gorge.
On the downside, I was disappointed how short the hike was. I think we went all the way from the north lot to the south lot and back (did the Gorge on the way down and the Indian Trail on the way back) and it took about an hour or so. If you are going to be driving from more than an hour away, you might be able to find areas around you that are really fun without having to drive so far, but if you're in Watkins Glen, this hike is a must.
My best advice: take an early morning hike with your hiking buddies, girlfriend, wife, etc. and then head out to the east part of seneca lake for some of the great wine tasting that they are known for! Definitely worth it! Then stay at one of the great B&B's in the area... we went there two years in a row now from 5 hours away! The second trip might have been even better, but we'll see how next year goes!