There are a number of differences depending on how far back you go. older slots that were made back in the 90s, unfortunately, have that look about them that scream cheap! However, some like that nostalgic look. Graphics and sound are the noticeable differences given that modern games can also come with high quality 3D rendering.
With the newer slots, you will find that there are more features that add to the entertainment factor. This means more random triggers, more bonus rounds, and more jackpot prizes to win.