I played the crap out of the first 4 games in the series growing up and just replayed this again. This game is still great and one of the best action platformers out there.

This is the classic Mega Man format cranked up to 11. Who knew adding a dash and wall jump (among other additions) would take Mega Man (and platforming) to a whole new level.

The soundtrack in this game is amazing, all the bosses are challenging but fair and the pixel art is top notch.

There are plenty of hidden upgrades and multiple ways to approach getting them or beating the bosses. Also an interesting and cool addition is how some of the stages change after beating certain bosses.

If you had a Super Nintendo growing up or if you're looking to play a classic this was and still is a must play.

This is the start of greatness, the first half to the best Sonic game in the series.

It does everything 2 does but better while also looking better than ever. New ability (split second shield), new ability shields (fire, electric, and bubble), fantastic music, and level design. This is also the game where Knucles is introduced to the series.

Can't forget the Chaos Emerald bonus stages. This version is easily the best in the series with the perfect amount of challenge and fun. (Looking at you terrible Sonic 2 bonus stages)
Getting into them is also more convenient all you have to do is find the massive hidden ring (no 50 rings needed). Multiple of these are hidden in each stage. Now, if you have 50 rings and pass a checkpoint, you are treated with another bonus stage that allows you to earn rings, shields, and extra lives.

This game is a blast from start to finish. The only downside is the small number of stages (6 Zones), but don't forget this is technically half a game that gets expanded with the next release in the series.