Well speaking in terms of visual details and game play not much. Classic slots are simple games with 3 reels and usually anywhere from 1 to 5 active pay lines. The game play is pretty dull at times since most of them have no bonus round installed. Most of them don’t even have a Wild symbol available, so if you’re used to playing modern video slots you can be taken aback by the simplicity of these games. But still classic slots can be quite lucrative at times since most of them have a rich pay table.
Another advantage is that you are only playing on a single or up to 5 active pay lines. So in fact you are betting pretty high per bet line. The top payout in many classic slots easily surpasses 5,000 times the total stake, so with some luck on your side you can have a pretty successful session on these games.
Today the number of classic slots at online casinos is pretty low. The provider which has the biggest number of classic slots is Microgaming, while other providers limit their offer to only a handful of classic slots. You can also find some classic slots which come with a progressive jackpot attached or a high top payout. Just like in any other slot game winning the progressive jackpot can prove to be a daunting task, but with some luck on your side nothing is impossible. In the end even a classic slot will pay if you’re persistent enough.