Yes, go downtown to see 'Old Vegas'. All the casinos are next to each other, much more walkable than the strip. Lots of bars on Fremont Street worth checking out. Uber/Lyft is your best way to get there from the strip. Cab rides are about $25 each way (I think). Don't waste your time on the bus.

Some of my favorites.

Atomic Liquors if you're into craft beer.
Pizza Rock
Cheap 2/4 limit poker at Flamingo
Ellis Island. This off strip casino is right behind Linq/Flamingo on Koval. Cheap brew they make themselves. Cheaper gambling limits. Restaurant is a great deal. Most will tell you to get the BBQ, I say the Metro Pizza stand is the right move. You will love or hate this place. I go multiple times every trip.

My pinball recommendations are in line with everyone else in this thread.

I would agree with many of the tips above except for what I quoted. Just depends on how much money you want to save. The bus ride does stop frequent and this makes for a very slow ride. Here's an idea of that trip.

For a first time visitor, walking the strip and popping into the different casinos can be part of the fun.

This is probably my best piece of advice. The casinos appear to be closer than they really are. The Rio may look walkable from the strip, but it's a LONG walk. When in doubt, take a cab/bus/car/etc. Again, Uber/Lyft is a great way to get around Vegas.

I think the Heart Attack Grill is literally right next to the new arcade. Banger Brewing is right there as well and is worth checking out also.

If you're a foodie, lots of great restaurants on Freemont Street. I really liked 'Eat'.

I think these are two great downtown options if you just want a basic meal.

If you want classic, no frills American diner food, Dupars in the Golden Gate is a nice choice. Especially for breakfast.

For really good bar food, check out the Chicago Brewing Company in the 4 Queens. Nice cheap video poker at their bar and they brew their own beer which is above average. Its comped if you're playing video poker - always a plus!

Directly behind Bally's. Flamingo is the street that runs right between The Flamingo/Cromwell casinos and Ballys. Walk right between them and you'll see it. It's a 10 minute walk.

On the way, if you're into the seedier side you can pop in the Stage Door. And that walk takes you right where Tupac was shot. (That said, its a safe walk).