Peggle is a fun casual game. It's very straightforward. Aim for the orange pegs. Hit the green ones to get various power ups that change every few levels. The power ups are all very different and keep things interesting. Some are not as useful as others like the lobster claw flippers. Each power up makes you think differently about how to approach a level.
As straightforward as the gameplay is, Peggle isn't simple. You only have 10 moves to clear all the orange pegs and it's difficult to predict just where your ball may bounce at times. Most of the time the results are what you aim for, but sometimes the judging an angle slightly wrong can turn into a wasted ball. Other times, you might just get a layout that works against you. While the design is always the same, the placement of orange pegs varies. But that's the challenge of Peggle.
There are 55 levels in the game, so plenty to play through. You can always replay levels of your choice later outside of story mode to try your hand at clearing the entire playing field of all blocks.
I wouldn't really consider Peggle a largely re-playable game. I played through story mode twice on a non-Steam version of the game, and playing through again on Steam didn't really hold my interest. But I would definitely consider this a great game for at least one or two playthroughs that is worth it's price point.
The only negative aspect of this game is the resolution, which is low and doesn't stretch to fit widescreen monitors.