See the NPS website for Guadalupe Mtns NP to get detailed trail information - this is my impression of the hike.
Make sure you wear sturdy hiking boots and have plenty of water - no water is available other than at the trailhead.
This hike is the main reason I came to the park and I'm glad I did! Originally, I planned to hike this route the day prior but with 50 mph winds predicted, I delayed this hike by a day and instead went to McKittrick Canyon (see other report). Anyway, the trail is 90% rocky - small, medium and large rocks of varied shapes. As can be imagined, you are climbing most of the way up along a trail that is not very wide but wide enough to walk easily on. The trail is easy to see and you cannot get lost.
I stopped numerous times to take photos and just look around. The altitude didn't bother me too much (I'm used to 2000 ft elevation) but a couple of times, I had to stop and take some deep breaths. The wind was blowing the entire time yet I was soaked in sweat by the time I reached the summit 3 hours and 45 minutes after I started.
I found a nice flat piece of rock and sat with some bushes behind me letting the sun dry my jacket and shirt. There were hikers already at the peak when I got there but when they left 20 minutes or so after I arrived, I had the peak to myself for 10 minutes before the next group arrived - solitude was not to be had. Nonetheless, I stayed another 5 - 10 minutes before heading back down myself. The return time was much shorter and I encountered no difficulties heading back.
Of note - while walking back, I was in a section of the trail that has coniferous trees on both sides when I smelled "cat". Looking around, I did not see either a bobcat or mountain lion but the smell was definitely in the air. The smell had not been there on my way up so I can only assume a cat of some size had passed by and marked his turf at two places separated by about a half mile or so.
I strongly suggest to anyone contemplating this hike to be as physically prepared as possible - hike as much as possible in rocky terrain with hills. Make sure you have plenty of water!! Unless you are trying to set some personal speed record, remember you are there to enjoy Nature - stop, look around and enjoy the sights!