Grill 55 is a little strange - it's a bar attached to the Renaissance Hotel (right near the lobby) near some live music on Fridays and a TV/Envy restaurant. You wouldn't expect much of it to be honest but surprisingly, it is a pretty interesting/solid restaurant if you're around the area.
Grill 55 is super casual (although I'd recommend sitting at the bar over a table). Seat yourself and grab a menu. The items aren't too numerous and seem pretty safe such as sandwiches and salads. However, the taste is surprisingly fresh and tasty. My favorite were the fish tacos which had a surprisingly spicy/tangy sauce in two nicely sized tacos with hot/fresh tasting white fish. It also came with fries or a salad. The presentation was also nice to see with the tacos being held up by a stand. I also had the grilled cheese one night which was also solid (although I wish they heated up the sandwich more to make the cheese completely melt). The tomato soup it came with was pretty good too. At the bar, don't forget that you get free spicy wontons (basically little tangy chips). The drink selection isn't too shabby with a mix of cocktails ($12) to beer/wine ($6+). They also have happy hour which I was never able to make it down by. Food items are a little pricey (ranging usually $12+) but in the context of Vegas food, it's not too badly priced.
Service was fairly friendly and it was nice to have the place open till 1AM so you can grab your late night fix. Seats were comfy - the AC was on full blast and there is even some music nearby if you come at the right time.
Again, don't go in with overly ambitious expectations of grandeur compared to the likes of some of the exquisitely designed (and pricey) restaurants of Vegas. However, for a late night (or earlier) snack, especially near LVH/the LV Convention Center which is devoid of a lot of good food by foot - Grill 55 is a god-send for affordable Vegas eating in the area.