Slot Machines grow in complexity. From simple three reels - like the ones seen in Casinos. To fruit machines with sub games - like those in Pubs.
If there's one game that the Internet can similate as good as the 'real' world then it's Slots. It's no secret that these machines run by pay-out percentages where a machine is set to pay out a certain percentage of what is taken rather than on a total random basis. The web works the same. Fruit Machine interfaces can be perfectly created for play over the web. The thrill of the spinning reels is still there and the skill in knowing when to stop remains.
Before you go on any online slot/fruit machine you should check to make sure the website has been vetted by an independant organisation for fair play. Most casino websites will tell you their minimum pay-out levels on the games - you'll find they mostly brag of this as it's often higher than in a 'real' casino/pub/arcade.