Knytt Stories
Knytt Stories has to be one of the most in-depth side-scrollers I've played. The music is great, the sprites and backgrounds are really well made. Plus, there are lots of great expansion packs!
Give it a try, I doubt you'll be disappointed!
Download: http://nifflas.ni2.se/index.php?main=02Knytt_Stories&sub=03Download (http://nifflas.ni2.se/index.php?main=02Knytt_Stories&sub=03Download)
This game is a sequel to Knytt (http://nifflas.ni2.se/index.php?main=03Knytt). I recommend that you play it before you try Knytt Stories.
Expansion Packs: http://nifflas.ni2.se/index.php?main=02Knytt_Stories&sub=04Get_More_Levels (http://nifflas.ni2.se/index.php?main=02Knytt_Stories&sub=04Get_More_Levels)
(http://nifflas.ni2.se/content/02Knytt_Stories/02Pictures/image1.png)(http://nifflas.ni2.se/content/02Knytt_Stories/02Pictures/image2.png)(http://nifflas.ni2.se/content/02Knytt_Stories/02Pictures/image3.png)
(http://nifflas.ni2.se/content/02Knytt_Stories/02Pictures/image4.png)(http://nifflas.ni2.se/content/02Knytt_Stories/02Pictures/image5.png)(http://nifflas.ni2.se/content/02Knytt_Stories/02Pictures/image6.png)