If you are looking for a classy, swanky Las Vegas experience. . . you are in the wrong place. haha.
Fremont Street is so amazing. There are so many weird shenanigans going on there and rough looking people. They always have live concerts going on and events. The ziplines I have yet to try, but will soon. The overhead screen is really something to behold. The overhead screen itself is worth making the trip for.
I go to Chinese New Year every year on Fremont Street and they have the most amazing overhead projection and music. Its beautiful. The street performers are super weird but are so interesting and I should note that if they make you stop and look, you owe them a dollar.
There is a lot of re-vamping going on down there these days, but what I like most about it is the old Las Vegas feel. I know this sounds weird, but being in the older casinos is kind of kick because you feel like you are back in time. I love the nostalgia of it all.
While you are down there you should definitely take a minute to check out the fish aquarium in the Golden Nugget. It has a waterslide from the pool that goes right through it.
I also recommend the italian restaurant right next to the aquarium. I have eaten there several times and the food is good.