Rating:  4 of 5 stars (for an off-season hike), less for a summer hike
Snow:  None.
Time: This trail took us (two 65-years-olds) 4 hours for the loop, including trips to Far Country Falls & Coal Creek Falls (both recommended!).
Views:  De Leo Wall Lookout is not worth it.  However, if you do the Viewpoint Trail (which runs parallel to the De Leo Wall Trail), the views are worth it.
Parking & Road Conditions:  No problem getting to the parking lot with any type of car.  No snow on the road.  Many parking spaces left around 10:30 on a Thursday at the Red Town parking lot. 
My opinions:  This was a fun “first of the season” hike. 
There are nice forest paths and nice small waterfalls.  Today there was snow and hail alongside the path.  Very beautiful!  Not a problem to hike on.
Trail conditions:  Great overall.  There were some muddy areas and the coal creek bridge was icy, but nothing bad.

Specifics on the hike (different from the WTA directions):  The hike from the Cougar Mountain Regional Wildland Park’s Red Town Trailhead to the De Leo Wall Peak is pretty straightforward: 
Follow the signs for Wildside Trail (W1) to the Marshall Hill Trail (W6) which becomes the De Leo Wall Trail (W9) after crossing a paved road. 
Also, after crossing the paved road, there is a sign that says,
DE LEO WALL TRAIL (up or “straight ahead” arrow)
CROSS TOWN TRAIL (right arrow)
VIEWPOINT TRAIL
Go right (and downhill).  Stay on the VIEWPOINT TRAIL.  There are a few places that the trail is pretty narrow.  Keep vigilant and you should be fine. 
The views along this trail are nice, much better than the De Leo Viewpoint. 
When you get to the Viewpoint, it is a disappointing view; however, the trail to the viewpoint is nice.
When you get to the sign for the Viewpoint Trail (0.2 miles) and De Leo Trail, go right. 
Next, connecting the De Leo Wall Trail (W9) to the different waterfalls is where the hike got really interesting. 
Continue down W9, pass W1 (Wildside Trail) on the left.  This trail will go back to the Red Town Trailhead.
W9 (De Leo Wall Trail) dead-ends on Indian Trail (W7), at a T intersection.  You can get to two waterfalls from here.
The first waterfall is a quick trip.  Go right on Indian Trial (W7) to Far Country Falls.
Go down W7 about 0.2 miles.  The top of Far Country Falls will be on your right.  There is an un-signed path to the top of the falls.  Nice place to look.    Continue on W7 for another 0.1 mile and there is a signed turn-off to Far Country Falls.  There is a great place for selfies with the water falls behind you.  Worth the trip!
For the second waterfall (Coal Creek Falls), go back to Indian Trail (W7) and turn left, back-tracking where you originally came from. 
Pass the De Leo Wall Trail (W9) and go about 0.6 miles to the Quarry Trail (C6) on your right. 
Climb up Quarry Trail (C6).  You will pass interesting boulders, going uphill for about a ½ of a mile and turn left on to Coal Creek Falls Trail (C4). 
After passing Coal Creek Falls, continue on C4 until you come to Cave Hole Trail (C3) and turn left. 
When there is a sharp left to stay on C3, go straight on C2, to see an old dam (Red Town Dam Site). 
When you get to Military Road (N2), turn left and follow the signs to the Parking Lot (.2 miles).
I printed these directions out when I hiked and they helped a lot!
About a 6 mile loop!
It’s worth studying the map on line before you go.
https://aqua.kingcounty.gov/gis/web/VMC/recreation/BCT_CougarMtn_brochure.pdf

My hiking group had a great urban winter hike today starting at Lake Boren Park. The restrooms were open, clean and stocked with supplies. It was a crisp 27 degrees when we started walking at 9:15 with clear blue skies. Our 6.3 mile loop started on the Newcastle trails and on up into Cougar Mtn Regional Park.  We followed the Powerline trail south from Lake Boren and then went left on the May Creek trail.  Once we reached Coal Creek Parkway we crossed over and took the Highland trail and went up past the old DeLeo homestead on an unmarked trail at the base of DeLeo.  After crossing into Cougar Mtn Trail system we followed the lower trail to the DeLeo Wall viewpoint and north to the Crosstown Trail reentering the Newcastle trail system.  We stopped for a mini rest / break at 11:15 near the viewpoint.  All the trails were frozen or with frost heaves but no real slippery areas, we only had to step over two downed trees.  Trail traffic was super light, we saw only one trail runner on our entire route.  At the Beit Tikvah temple we we followed SE 79th Pl back down to Coal Creek Park Way and made our way around the north end of Lake Boren past Aegis Gardens.  We saw many bird species; creepers, juncos and crows and around Lake Boren - red winged blackbirds, grebes, egrets and ducks.  Another fantastic day to be out in nature with friends.

We were driving up to Bellevue when it all of a sudden started snowing and traffic slowed to a near-standstill. So we decided we needed to get out of traffic and get onto a trail. We took exit 7 off 405 and headed over to Coal Creek. There were quite a few cars there, but it had only been snowing for 15 minutes and there were definitely less when we left. Grabbed raincoats from the trunk and with coffees in hand (in Gore-Tex mittens) headed up the trail. Snow was accumulating on the cars already! Big flakes were falling and once in awhile went right up a nostril or rested on eyelashes. It was great! By the time we finished it was very lightly raining. Did 2.5 miles or so. We were glad to have been able to get out!

We had a delightful wintry walk from Lake Boren to DeLeo Wall for a 6.2 mile loop. The restroom facilities are open, clean and stocked with supplies.  Skies were overcast and is was 31 degrees when we headed out.  About 1/2 inch of snow was on the ground at Lake Boren Park when we started walking south on the Waterline trail.  Next we took a left on the May Creek Trail following it down to the creek and back up to Coal Creek Parkway.  After that we took the Highland Trail following it to the second water retention post where we keep going straight.  The trail passes the old DeLeo family home now abandoned and in a heap left to nature.  There is evidence of new road construction and tree removal just north of here.  We followed a lesser, narrow trail at the base of DeLeo Wall all the way up to Cougar Mtn Park. Once in the park we took a left and followed that to the viewpoint.  Low cloud cover made territorial views unremarkable today.  The trail becomes narrow with a several hundred feet drop off as you head north to the Crosstown and Terrace Trails. Tread lightly if you don’t like heights.  Snow was deeper up here and made the walk feel magical.  We followed the Crosstown trail back down to Lake Boren.  Thanks to whoever has been working on the trail here!  You work is much appreciated - dips leveled out, wider trail supported with rocks on the downhill side and side drainages improved. Kudos to you.  Trail traffic was super light a couple dog walkers on the Crosstown and Waterline trails.  No wildlife sightings except a few birds.  Another fantastic day to be out in nature with friends.

Great little hike close to Seattle! Trail in good condition, not even muddy. For some variety on the way down, I stopped by the meadow restoration area and went down the Red Town trail and Rainbow Town trail (where there's an old mine shaft). Only saw faint traces of snow around this section.