XS is cool. I went on a Sunday night so it may have been an off night. I got there at 11:30 and there were around 50 people or so waiting around in line. I went up to the front and talked to a guy with a clipboard and told him that I'm on the guest list. He found my name and let me (guy) and my friend (girl) in with no problem. I was very polite to him and he was cool to me. I also had a free admission pass and they took it with no problems or hassles. I'm pretty sure that this is because it was a Sunday so YMMV.
The club looks just like Tryst. I think the layout is almost identical. Sure XS as the stripper poles, etc. but overall the layout is pretty much the same. I like how it opens up to the pool since it gets so freaking hot inside these Vegas clubs. I don't know what it will be like in the summer but I'm guessing not so good.
Overall, a nice experience and environment.
The crowd was pretty good but there were a few odd really old guys (like 70 years old) going nuts on the dance floor.
The music was mediocre at best. The DJ played mostly house/trance and sometimes mixed in some hip hop. The worst was the random gaps lasting 3-5 seconds of just pure silence between mixes. Everyone on the dance floor basically just looked at each other until the next song started.
Overall, good party vibe though for a Sunday night. I like the crowd at Tryst and Pure much more.