I can't tell you what the ten best hikes in the country are, but I can tell you what the worst hikes I've done are. All of these hikes were more than merely uninteresting. Some are bad hikes, even under ideal conditions. A few were just marred by unfortunate events.
Peninsula Trail or Sycamore Loop, Indiana. Okay, I did both of these the same weekend and didn't take pictures, so I can't remember which trail it was that was second-growth forest. Young forest isn't unusual, but what made this hike so dreary was that the trees had been planted in rows.
Land Between the Lakes, Tennessee. I've never been able to warm up to this area. I don't find it particularly scenic, but it is particularly ticky. Coming from Nashville, at least, there are so many other better choices that are closer.
Fall Creek Falls, Tennessee. Lovely area. Even this trip had its good parts, like playing in the waterfalls. However, our hike was cut short by angry hornets that scattered our party into two groups and left most of the group nursing stings. (This was after our close encounter with a copperhead.)
Cedars of Lebanon, Tennessee. This is a pretty nice park, and I like the cedar glades of Middle Tennessee. But I did a solo hike there one time where the trail was incredibly poorly marked and, even worse, liberally criss-crossed with spiderwebs. I had the heebie-jeebies for weeks after coming eyeball-to-eyeball with so many spiders.
Pelham Bay, New York. If you take public transit to this hike, you have a 50% chance of being run over as you walk the shoulderless road with cars blazing by just to reach the trailhead. The trail itself is in desperate need of maintenance. Even if it were cleaned up, though, there wouldn't be much "there" there.
Water Valley Overlook, Tennessee. This section of the Natchez Trace was so unpleasant we actually elected to return by the road. The biggest problem, besides few rewards, is that it is also a heavily-used horse trail, and every quarter-mile or so you have to stop to shake mud off of your unbearably heavy boots. Don't do this one barefoot. Pro tip: Leave horse trails to the horses if they get heavy use.
Pennyrile Trail, Kentucky. 13.5 miles, and only the first two or so are remotely interesting. Worse, the trail was created by one man with a vision. Cool in theory, but in practice the trail isn't properly built or maintained, so for about ten of those miles you're walking with one foot higher than the other.