My son (14) and I (50) hiked this on a rainy June day, despite checking out the weather forecasts every day for a week in hopes of choosing a sunny day. Despite a forecast of "clear" for both the AM and PM hours, we walked in rain for much of the hike, with clouds the rest of the time. Sadly, we had virtually NO view once we reached the top. But, that's mountain weather for you - you never know in the Adirondacks. It did clear up once we got back to the truck, however. Sigh. But hey, my main concern - thunderstorms - which we had EVERY day at our campsite in Lake George, never were a threat.
We're just occasional hikers but are reasonably active; as part of a "health wake-up call" in 2012 I started running a few times a week and doing some occasional 5K's. While I'm guessing you use some different muscles when hiking vs. running, the running has definitely helped me out a lot on longer hikes and I'm certainly doing less heavy breathing than on past hikes. Being relatively new to "real" hiking, our only other hikes of much consequence besides Marcy was Algonquin Peak in 2012 and Mt. Washington in 2011.
We did the Marcy hike in one day via the Van Hoevenberg Trail (VHT) from the Adirondack Loj (AL) parking lot, after getting up early for the 90-minute drive from Lake George. We signed the first log book (there's another near Marcy Dam) at 8:15am and signed out at 6:45pm, so we were on the trail for about 10.5 hours. We spent only about half an hour on the summit, eating some granola, drinking water, snapping some pix, and just having some father-son chats. We probably stopped a dozen times on the way up for some quick breathers/water breaks but only about half that on the way down. I had visions of pizza and beer in my head the whole way down and wasn't going to delay that any more than necessary!
The first two miles, from the Loj trailhead to Marcy Dam, is an easy walk in the woods, with mostly dirt trails, some planks over water-logged areas, and a walkway through a marshy area with a bunch of dead trees. After signing in a second time near Marcy Dam, the trail becomes rockier as we approached 3,000 feet. From 3,000 feet to 4,000, the trail becomes progressively rockier, but you can usually walk between the rocks instead of hopping from one to the next. After 4,000 feet or so, however, it's pretty much all rock, and bigger ones at that. Somewhere around 5,000 feet, as you enter the alpine zone, the trees become stunted and eventually disappear completely and you're hiking up rock slabs to the summit, which is bare rock. While every inch of the trail was wet below 5,000 feet and the trail often included a little stream of water that accompanied our journey, the wind near the top thankfully dried out the bare slabs above that. Oh yeah - there is a false summit a couple hundred feet below the actual top that can prove to be a little disheartening as you think you've reached the top, only to realize you have a couple hundred more feet to hike up.
There wasn't much to report from the summit, as the aforementioned rainy weather and complete cloud cover prevented any decent views except for a brief teaser, when a couple of clouds parted just slightly for a minute or so, giving us a cherished but all-too-brief glimpse of some other nearby peaks.
As mentioned, we did Algonquin the year before (2012). Lots of folks seem to want to know how they compare. Marcy is quite a bit longer (7.6 vs. 3.9 miles, one-way) and you have 230' more elevation to ascend. (I've found different mileage on web sites vs. the actual trail signs, perhaps owing to modified/rerouted trails.) For both, we started off on the VHT from the AL trailhead near Heart Lake. The trail splits after about .9 miles - Marcy to the left, Algonquin to the right. From the split you ascend about 3,200' over 6.7 miles for Marcy and about 3,000' in only 3.0 miles for Algonquin (according to the sign). However, it's really flat from the split to Marcy Dam, probably only 200' in elevation increase, so it's more like 3,000' in 5.5 for Marcy. So, even with that flat section on Marcy, Algonquin is quite a bit steeper and doesn't have very many relatively flat sections mixed in like Marcy does. There were two other factors that make a comparison difficult - 1) I was 15 lbs. lighter and in better cardio shape for Marcy vs. Algonquin and 2) I had hiking poles on Marcy but not Algonquin and they help out A LOT on the descent. Bottom line is that both are relatively tough - both Marcy's mileage and Algonquin's constant steepness wear on you and your legs may very well be sore for days afterwards, if you're an old fart like me.
Gear-wise, my son had a small Camelback pack with three extra collapsible liter bags of water and some essentials (compass, headlamp, bug spray), while I carried a larger Camelback with yet more water and stuff - GPS, sunscreen, more bug spray, spare batteries for headlamps/phones/GPS, snacks, head nets for bugs (didn't need 'em), headlamps, emergency blankets, rope, extra socks, waterproof jackets, first aid kit, water purification gear, survival knife, bear spray (probably overkill, but I don't take chances when my son is with me), etc. Mine was probably 25 pounds, my son's about ten.
We wound up carrying too much water (probably 1.5 gallons in all) but had the sun been out and hotter, we probably would have used every bit of it. You will be near water for much of the first half of the hike, so next time I'll probably take up less water and just use my purification kit to refill. Once you're about halfway up, however, your water-refilling options greatly diminish. As with all the stuff I hauled up, it was better to have the extra water and not use it than to need it and not have it, I suppose.
We both had waterproof Merrell boots but both pairs eventually became water-logged after a couple of deep puddles and hundreds of steps in deep mud. On a dryer day, I think our feet would have stayed nice and dry.
Anyway, we'll pick another peak next year, maybe Haystack or Skylight, though Giant might be a nice (and comparatively easy) choice too. Just want to have a view on one of these hikes!