I've gone to Pho Kim Long a few times while visiting friends in Vegas. It's right there on Spring Mountain Road, which is very busy decked out with restaurants and stores.
At times this place gets really busy. But it usually doesn't take too long to get in. I've tried the beef cubes which are amazing as well as their pho. They do it really well here. Last time I visited we also got the salt and pepper shrimp. YUM. I would say that is a must try.
This place is definitely one of my favorite spots to eat in Vegas. Best part is that they're open 24 hours as well!