Here's my personal favourite homebrew / hack games in order of favourite to least favourite (I'm probably missing a bunch which I'll add later)
This is the best video game hack ever made. I've never found another hack that even comes close to being as fun as this game! So much is changed and the stages are so brilliantly designed you'll never get bored playing this.
I actually used to roommate with chris emerzian the guy who made this game. But I'll be honest the game used to suck then he added a lot of stuff to it now it's FREAKEN AMAZING!!!
XOP Black Ultra:
Sequel to the original XOP. I actually beta tested this game before it was released and gave a lot of advice (I insisted that the huge butterfly must flap its wings!). I'm not in the credits but I suppose in todays dog-eat-dog world people never get respect for their ideas. Still though atleast Chris listened to my recommendations and implemented them into his game making it fully A.D.D. friendly!
D-pad Hero 2:
Now this was an interesting discovery. D-pad hero 1....well....IT SUCKS. However d-pad hero 2 is everything that the first game should have been. They made the game easier to learn so it's actually fun to play!
Super Bat Puncher:
This nes homebrew is extremely good and it was hard to decide between this and d-pad hero 2 for spot #3. But overall I found d-pad hero 2 to be more addictive. This is probably the most polished homebrew I've found for the nes. Graphics are smooth, the screen scrolls, the music is well made (too bad there's not more songs), and the programming is tight!
Battle Kid: Fortress of Peril
This is the most complicated looking homebrew nes game I've ever seen. I'll be honest I'm not a huge fan of this game (lack of scrolling and music that annoys me) but it's still a truly amazing product that everyone should play.