The first mile or so of the trail is mostly nondescript and steep. The trail is wide but lined by alder and some pine making the scenery not much to look at. Once you get above the alders, you get some fantastic views looking back towards Whittier.
Upon reaching the top of the pass, climbing around 800 feet in a mile and a half, Portage Glacier and Portage Lake come into view. Of course, it really is an awe inspiring sight. Just this one view was well worth the effort of climbing the mile and a half. All around the top of the pass are side trails to explore, if you're so inclined. There are numerous scenic overlooks, massive displays of waterfalls coming off the valley walls.
Many hikers turn around here and call this good enough, or you can continue down the back side of the pass to the lake. This side is a more gradual descent than the initial climb up to the pass. This section of trail gets narrow and a bit overgrown in places, but it's easy to follow.
I am not sure why but there is very little information online about this hike which is strange since it is obviously well traveled. I saw at least 30 people on the trail. I even saw a seventy five year old woman three quarters of the way up as I went back down. If she can do it so can you!
Kids on this hike are no problem as long as you don't wander too far east on the glacial rifts. It becomes too technical and there is a sudden and unexpected drop off into a river valley. If you take the train be prepared to add 3 miles total on the hike to and from Whittier. Spend the night if you can and leave for the trail later in the day to get the best photographic material.
Take water with you if you do not know how to find safe water. There is not water available near the pass. You will have to hike down towards the lake to get to some, or go back to Whittier.
Bug dope is not necessary if you do not go farther down into the valley. If you do you will be sorry if you left it at home.
Watch the well hidden potholes on top of the pass off the beaten path. They will swallow your foot whole.
The tunnel in and out of Whittier, "The Strangest Town in Alaska" has a toll of $13 per vehicle, though you only pay going into Whittier, not leaving. It opens on the half hour from the Portage side, on the hour from the Whittier side. More information on the Whittier tunnel can be found here.
If you'd like to educate yourself about glaciers and their awesome power, please visit All About Glaciers, a great introductory website.