Sushi is vinegared rice. There are 2 main types of sushi you will eat in a sushi restaurant: nigiri sushi (formed with the hand) and maki sushi (rolled in a sheet of seaweed). There are other sushi dishes, but you won't get them in a sushi restaurant.
Sushi is made by cooking the rice, simultaneously cooling the cooked rice and reducing the moisture content, cutting in the vinegar/sugar/salt mixture and then finally forming the rice into a shape. Some of these things can be done well in an automated process, some of them can not.
To make very good sushi, you need to understand the rice. Rice is all slightly different and it will contain more or less starch, have more or less bran still attached to the kernel, etc, etc. When you start you need to inspect the rice, wash it appropriately and choose the correct amount of water to cook it with. How well you do this step makes a surprisingly large difference in the end product. If you don't wash off the starch well enough, it will end up gluey. If you don't polish off the bran, you will get rancid flavours. If you don't choose the correct amount of water, you will get mushy rice. The list goes on and on (I'm by no means an expert, but I've failed to make great sushi on enough occasions to at least enumerate some of my failures ;-) ).
Generally speaking, if you buy sushi at a kaiten sushi place -- or even just a place that just isn't very good, they aren't going to get this step right because it takes experience and attention to detail. Big kaiten sushi chains are going to select a forgiving rice. They are going to wash it exactly the same way each time. And they will get a relatively consistent, but not very good result.
The next bit is cooking. This one is perfectly suited to automation. If you get the rice to water ratio correct, modern rice cookers cook rice virtually perfectly. From Jiro Dreams of Sushi, I know they use their jury rigged pressure cooker setup, but TBH, I'm a bit skeptical that it makes all that much difference. He says that he has to do it under pressure because of the rice variety, but I'm not sure why he can't use a normal pressure cooker -- probably because that's just not the way he does things.
Anyway, once the rice is cooked, you need to cool it to a precise temperature while at the same time reducing the humidity. This is really hard to do well. If you get it wrong, you will either get too hard a texture, or more likely mush. However, it's the kind of thing that machines are really good at.
The next step is really hard to do well with a machine, I think. While maintaining the correct temperature, you need to mix in the vinegar mixture. The technique you use to mix the vinegar, the speed that you mix it, the amount that you use -- all depends on what the rice is doing that day. It depends on the ambient temperature and humidity. It depends on how well you've washed the rice. It depends on how perfectly you got the water/rice ratio when you were cooking. If you get it wrong, you will range from crumbly, falling apart sushi to glue. Machines do this very poorly, it seems. They uniformly under-vinegar the rice. I think it's because when they are extruding the rice (in the next step), they need the rice to be firmer than you would if you were doing it by hand.
First you need to keep the sushi rice around before use. You can't really have a continuous cooking process, so you need to cook in batches. However, as the rice cools, the starch forms crystals. This causes the rice to taste dry and to have a rough texture. You need to maintain a consistent temperature -- not too high because it will continue cooking, not too low because it will crystalise. You also have to maintain the proper humidity. There is nothing that makes this harder or easier for automation, but it depends on how you are moving the rice from one place to another.
Finally, you have to form the rice. As I said, there are two main kinds of sushi that you will have at a sushi restaurant. The one that many North Americans are most familiar with is maki sushi. This one is dramatically easier to make. You spread the rice on a piece of nori seaweed and roll it up.
To understand how to do this well, you have to understand that rice has a flavour. It is a very subtle flavour, but a flavour nonetheless. Japanese meals are not like western meals. You don't have "main dishes" with fillers like potatoes and bread. Instead, the main dish is rice. Everything else is a "side dish" and is meant to accentuate the flavour of the rice. This is why Japanese food is so delicately flavoured, without strong herbs or spices. It's also why you eat the rice without salt or some kind of sauce.
With maki sushi, you have a piece of roasted nori that adds some crispness and earthiness. Then you have a filling that should accent the rice. The problem is that if the rice is mushed up together, it tastes like glue (umm... well, it literally is glue at that point). To get the flavour of the rice to come out, the most important point is air! Each kernel of rice needs to have air around it. At the same time, you need moisture, so that it has a good texture, sticks together, and creates a kind of sauce in your mouth (mixing the nori, rice and filling together). It's that balance of rice, air, water, filling and nori that is important to getting something that has nice flavour and then dissolves in your mouth, with a satisfying, mouth feeling texture and flavour.
Like I said, maki sushi is dramatically easier to do than nigiri sushi. That's because you spread the rice on the nori. This automatically creates both places for air and water to exist. Then you add the filling and roll up the nori. The nori then protects the sushi from drying out. Machines are extremely good at making maki sushi, IMHO.
Nigiri sushi is much more difficult. With nigiri sushi, you wet you hands (just enough), take a small handful of rice, form the rice into a rectangle, add wasabi (if you are going to do it) and then apply the topping (usually sashimi -- raw, sliced fish). Getting a machine to produce nigiri sushi at all is a triumph of engineering. However, it is uniformly awful. Instead of making a 2 dimensional object and then rolling it (to trap both air and water), you need to make a 3 dimensional object, with water surrounding the rice kernels and air in between. It has to be compressed just right so that it sticks together, while at the same time retaining the air pockets and water pockets. Then you have to apply the topping so that it sticks to the rice, so that when you bite it, it seems like one thing as opposed to falling apart in pieces in your mouth.
Good nigiri sushi seems to melt in your mouth. The flavour of the fish mixes with the flavour of the rice and washes down your throat. There are many different ways nigiri sushi can be bad, but the main ones are "piece of fish sitting on a pile of glue" and "a bunch of random junk that falls apart in your mouth in a sticky, mealy way". Machine made nigiri sushi tends to be the latter.
Having said all that, there are some caveats. The convenience stores sell "onigiri", which are triangular shapes rice balls wrapped in nori, with some kind of filling. They are universally awesome, even though they are made by machine. There are onigiri restaurants where they make everything by hand and they are admittedly better, but not nearly as much as hand made nigiri sushi vs machine made nigiri sushi.
And finally, I've taken some friends to very, very good sushi restaurants in Japan before (I live in a fishing village and we're lucky to have a couple of good sushi restaurants). Usually they are blown away. Occasionally they are, "Meh. Fish on rice. I don't really see the difference other than the price tag". So without knowing you, I can't tell for certain that you would care about the difference.