Stupid me, I quit at level 44 before realizing there were only 45 levels. Oh well...
For 2004 this is plays pretty smoothly and still manages to be enjoyable nearly 20 years later. It is simple, but that's the point of a demo, right? Plenty of obvious things to change here, namely the music, textured walls, etc. but the core physics feel good, if a bit frustrating for some of the more difficult levels.