The trains were always on time, clean and quiet. Also, the ride is sooooo smooth. It feels almost as though you're floating.
You'll want to plan your trip to get the most mileage out of your Japan Rail Pass which is only available to foreign visitors in Japan and can only be purchased outside of the country.
The passes are sold in weekly increments and the cost jumps significantly with each week, so if you can plan your trip so that all of your rail travel can be lumped together to avoid purchasing a longer pass that'll save you some Yen for important things like sake.
There are a number of important notes and restrictions so please take some time to review the information they've posted on their website to avoid any disappoint when you arrive.
The biggest decision for us was always whether or not to reserve our seats ahead of time. Sometimes we did and others we just showed up. We always got on a train and only once were we unable to find seats until a few stops in. That was the train between Osaka and Hiroshima. It was BUS-Y! So if you're trying to decide whether or not to reserve a seat, reserve it for this train.
And please remember that you're traveling in a foreign country, so the signs won't always be in English although many of them are. You'll benefit from doing a little planning before hand and the Japan Rail Map app is excellent for checking routes and timetables. It is also proper etiquette in Japan to wait for everyone to get off the train before trying to get on, so please remember your manners.
(have a good journey)