Luigi's Lost Levels is a short Kaizo romhack, compiling 5 levels that I designed for a bigger but abandoned project.
You can expect infinite lives, a quick retry system, custom graphics & musics, a challenge and, hopefully, a decent amount of fun!
I really enjoyed this hack. It took me seven hours without save-states.
It requires moderate use of advanced tech (shell jumps, regrabs, bubble jumps, and thwomp jumps) and Yoshi glitches, but is not too hard if you know to do them (with the exception of one jump in level 4, which seems disproportionately hard).