There are no roads to this WHS, so for a visit, you have to walk in from the nearest airport - it's 2 days from Lukla. Although there supposedly are helicopter flights nowadays that take you straight to Everest Base Camp and skip all the hiking! I went on foot and did an 8-day trek known as the Everest View Lodge Trek.
I had never hiked for such a long period on end before, but in retrospect felt it was pretty easy. Day walks were never longer than 5-6 hours including lunch and plenty of rest. This trek is the same as the first part of the one to Everest Base Camp. I think I could have made it there too but must say that I already was pretty bored after 5 days. It was early in the season, not many other travellers around, and several shops/restaurants/lodges were closed. And cold it was during the night: I needed a sleeping bag plus 2 blankets! Every night we went to bed at 7.30 pm because of the cold, and because there's nothing to do in the villages.
The forte of the park and the trek clearly are the mountain panoramas. The sky was clear blue on most of the days, and I saw Everest no less than 4 times (once already on the flight in from Kathmandu). The first half of the hike from Namche Bazaar to Tengboche had the best views of Ama Dablam, Lhotse and other 7000-ers. The local flora (not in bloom) and fauna (scarce except for black crows) I found not too exciting. Despite its remoteness, about 30,000 people a year visit the park.
Leaving often is the hardest thing on a trek from Lukla, and so it was for me. On the day I was to fly back to Kathmandu, one big cloud covered the valley (although the sky was blue and the sun was shining). The day before there also had been no flights, and it was anyone's guess how it would be tomorrow. So I accepted an offer to take a helicopter back down to Kathmandu for 150 US dollars - a sum I would have paid alone just for the experience to once sit in a helicopter!