Since there appeared the first slots (it happened in 1895), they gain more popularity. Today their appearance is of much importance- art graphics is an important entertainment element, the animations and sound effects, which significantly improves mood during game, are popular.
Graphics of high quality is used in modern slots; they often have 5 barrels, instead of obsolete slots with three drums. Essentially, this implies that chances of winning are increased, because modern slots always have more than one active line, i.e. chances of winning combinations of symbols is significantly higher.
Also slots in online casinos often become more complex due to number of active lines; it is desirable for beginners to keep to slots, having no more than 9-15 paylines.
While 3-barrel slots have only one active line, well, a maximum of five, some slots nowadays have up to 100 lines! Evidently, modern slots in online casinos are diverse and high tech.
Slots also have many bonus fillers, such as multipliers, wild symbols, and scatter symbols, or a possibility of doubling or even a 4-fold increase of your winnings, but no one excludes possibility of losing all money. Some progressive slots also hold a gambler, dreaming to get a big jackpot, at the slot.