Fer starters, I'm not a big fan of Tom Cruise. With that out of the way, him being in the film really didn't add or detract from the movie. Well, except for the one scene where he strides out of the house in samurai armor. Almost fell out of my seat laughing at that one.
Overall, it reminded me a lot more of Dances with Wolves than Shogun. It was more of a passing of culture story than an action flick.
If you no nothing at all about Japanese or American history (ala Trail of Tears kinda stuff), LS is still a good movie. If you know a bit of history, it makes it better in that you can pick up on a lot of the more subtle underlying stories. Things like the big change in culture when Japan outlawed the wearing of swords. How Native Americans were portrayed to the general public, etc.
If you like Japanese history or Kurosawa films, you'll probably like it. If you're looking for 2+ hours of people running around with swords chopping people up, you're butts gonna get numb along with your brain.