The example of expanding on a already successful formula
The third game on the Super Mario series is one of the best examples in gaming history of how to take a game that is already great and make some upgrades to it's sequel, making it still fresh, challenging and fun. The large number of outfits, giving it a very unique change of pace to the game, with so many variables on the gameplay was stunning when it first came out.
The game also expanded on the number of secrets you could find throughout the levels, being warps or bonus-zones, giving you something else to look for and more reasons to keep playing the game, even after finishing it. Another big thing was the over-world. For the first time we had some sort of a table top view on a map, which you could go from a level to another, seeing your progression and knowing when you could go to a castle or a bonus-level. Even with some pipes to help you travel around.
Alot of people consider this the best Mario game ever, heck, some people think this is the best GAME ever. So it's safe to play it's a must play game, being one of the best platformers you could possibly imagine, with awesome controls and the most famous character in video games.
