My 10 year old son and I hiked the TMT from south to north on Saturday. The weather was great, and we had a good time.
If you are considering hiking the TMT, be sure to bring a proper map. Particularly at the south end of the TMT, it can be difficult to ensure that you are on the right trail. While on the map it looks like it would be harder to stay on the TMT as you head north, it actually gets easier, because the signage gets better - at least in that direction.
For us, the difficultly finding the trail started right at the trailhead. The trailhead at the south end is just a pull out on Tiger Mountain Rd, just above Issaquah-Hobart Rd. The trailhead itself is a little further up the road, to the right. It's easy to miss.
The trail itself is mostly a slow climb through the woods to ~2500 ft, which given the grade is pretty easy. Although at 16 miles, it's pretty long. I found it less challenging than Mt Si which we hiked a couple of weeks earlier, but my son thought it was more difficult because it was so long.
While we did enjoy most of the hike, large sections of the middle ~8 miles were very overgrown. This had both of us putting on long pants and long sleeve shirts in the middle of a hot day, to avoid getting scratched up. It can also be very slow going through the brush. I am glad that I had the extra clothes in our pack.
One of the highlights of the middle section was "Dieter's Spring", right by the path. It was exciting for my boy to see a stream gushing right out of the ground like that, and it's something that I am sure he will remember for a long time.
For me though, I thought the nicest section was at the end of the hike, as it winds through a bunch of streams and across a number of bridges, well beneath a high canopy.
If you are looking for a nice, long hike, and don't mind push through the bushes sometimes, this one is for you.