To be honest, this just isn't a very good romhack. I like the idea of making retro-styled levels, but what exists here is lackluster at best.
"Other Power Star" has horrendous music with repetitive gameplay and haphazardly placed platforms that look out of place and only exist because the creator couldn't create any unique terrain. The background is bland, with most of your screen being filled with pure blue. It could really do with some background elements to uplift the atmosphere.
"The Retro Cave" looks okay visually, I get what the creator was going for with making most textures blue, but it starts to shift from looking just alright to looking disgusting, specifically in the town area with the red coins. In terms of gameplay, it has some difficulty with a number of gaps being filled with more placeholder platforms that make things sluggish.
The best part of this romhack imo is the custom pipe model that's almost forgotten about in The Retro Cave until it's brought back via a warp to the town area. I can't recommend this to anyone.