As I entered SLS from the valet doors, I felt like I was entering a club with the lit floors. I walked slowly through the casino and noticed that they put way too many a lot machines in, forcing people to have to step aside or bump into each other just to get through the casino.
The ceilings are low and have a warehouse feel. The interior is much like Hard Rock Hotel's renovation but with the unique touch of art like Cosmopolitan, I personally prefer being original. The carpeted floors are very cushioned so ladies please use caution when doing the horse walk. The overall flow is easy to navigate and the interior of each bar and restaurant offers an inviting feel.
As for the crowd, expect typical Vegas. While this hotel did just open so most employees should be on their A game, I will add that so far each of the people I have interacted with have been very polite.
It's worth checking out just to say you've been there. I am a local and not staying at the hotel tonight so I can not speak to interior and cleanliness of the rooms. I will update when I do stay with SLS in the future.