I'll try to give this place the benefit of a doubt. More or less leaning towards 3.5 stars solely because of it's convenience and pricing.
When staying at the RIO a lot of their food options don't open until 4pm or so (lame) so you are generally limited in your options unless you go offsite, room service, etc. Plus, when you're in Vegas for more than just a couple days, one can appreciate that you aren't going to pay a small fortune by eating at Smashburger.
I got a classic smash with fries. The fries...I'm sorry folks, these were awful. Cold...pre-frozen, flavorless.
The burger itself wasn't too bad. The house sauce is tasty and it was just the perfect amount. Beef patty was decently seasoned and the toppings were fresh. If I had to eat again, I'd just order something without the fries, no biggie. One cool thing about this place is that the receipt held a code for $2 off your next purchase (within a few days time) which I suppose is nice.
This place is nothing to write home about and am a little sad they didn't really have options outside of a burger but you can't really complain when you can get a full meal for under $15.