Disclaimer: Have never been to Japan or what I guess would be an "authentic" sushi bar. But I've been to a hell of a lot of sushi places in the US.
I figure sushi bars or restaurants come in two varieties, for starters: classic and modern.
Sushi used to be a high-end affair in the states. But then sometime around the mid-80s it became popularized and more modernized, and somewhat more affordable. If you have big appetites, 4 people can still easily drop $100+ on a meal for all.
To me, a classic sushi bar would serve the basics: miso soup (bean curd soup.) Nigiri (cutlets of fish over rice) and rolls (cuts of fish wrapped in rice then wrapped in seaweed rolls, sliced into cylinders.) Nigiri is true classic sushi. Rolls are less common in Japan than they are here. Said sushi rolls would have very basic, very traditional composition. (Fish, rice, wasabi paste, the sea weed roll.) There's simple variations to the formula too, like Sashimi (which is the raw meat sliced very thin into cutlets and served on its own without rice) or Bento Boxes (which is basically a little bit of everything and some rice served to the customer in a small box), which are common and easy and so most places have them. Depending on where the place is and how traditional it's trying to be, they may or may not offer other things besides sushi. (Chinese food usually fills in the menu because not everyone likes raw sea food.) The decor would be smaller, quieter, more intimate and private, with full booths separating you from other customers. Seating is likely limited because they're not trying to cram 40 tables worth of customers in. You might get personal contact with your sushi chef or they might do something special for you if they know you. They might be eccentric in their own way and have their own house rules about food, behavior and so on. The style of the place is likely plain or rustic. The quality of service might be all over the place depending on how it's run, because smaller operations tend to march to the beat of the owner. They will offer Sake (Japanese Rice Wine) of several different kinds.
Modern would be all that, with the following: a larger variety of rolls, and a way higher variety of what goes in rolls (avocado, cream cheese, crunchy vegetables and various sweet, spicy and savory sauces.) There's probably a roll named after the local sports team (The Husker Roll, The Hawk Eye Roll), and many rolls with bombastic names (like the The Dynamite Roll or The Kamikaze Roll or the Ninja Roll.) They'd likely also include a full Chinese food menu, tempura, and other classic hot Japanese dishes like Yaki-soba or Ramen. They might also have hibachi grilles with the guys who make a performance out of cooking your food on flat top (the performance, I'm told, is an American invention and Hibachi Grilles are not that common in Japan.) Depending on the place they might not offer as many specific kinds of sushi like Sashimi. But generally most sushi restaurants have plenty of variety in the kind of sushi they do, and most do the classics. For example, I've never been to a sushi place that didn't offer Unagi (cooked freshwater eel drizzled in Eel Sauce. OMFG GOD IT'S LIKE EATING HEAVEN OMNOMONOMNOMONOM.) The decor would be a lot closer to a modern restaurant, with closely set tables and less to little privacy. There might be gimmicks such as a motorized set of boats circling the chef's work area for them to lay out food on. The place is probably huge to accommodate lots of customers. You're not likely to talk to your chefs or know them personally, and so are less likely to get that personal treatment. The place is probably less based around the idiosyncratic nature of individual chefs or owners. The style of the place is probably loud and bombastic (sake bombs are probably heavily promoted), edgy and hip (muted lighting, everyone wears black and there might be leather couches and low tables rather than straight up dining tables), or rather large and "big chinese restaurant" in imagery and aesthetics (because this is America and people probably don't know or care what the difference is, they just know "that's Asian" and that they just want sushi.) You'll probably get average service at least, or in the case of some really snazzy and hep sushi places, the waiters might be to sushi what sommeliers are to wine. Which can either be enlightening or really obnoxious. They will offer sake, and it will undoubtedly be Gekkeikan at a minimum (it's the most well-known sake and also the cheapest.) The nicer the place, the better and more expensive the sake they will offer. (I really love unfiltered sake that still has rice pulp in it. Most sakes are clear.) I also prefer sake hot because it's has much more body and aroma and flavor. Cold sake barely tastes like alcohol and has none of the richness to it. But I've had some snooty waiters (or cooks I suppose) refuse to warm up certain sakes for me.
And FWIW, I live in the midwest of all places. So I probably don't even know what real cutting edge sushi tastes like since "fresh" is, ahem, debatable when you're as far from a coast as you can possibly fucking be in America.