Half-Life: Decay Singularity is actually doing fine. I decided to play just to have some more of it. It just crashed once other that I completed it. I suggested everyone who wants to go for it. You can save anywhere you want, and you are playing as Gina. But don't forget not all areas are connected so after every mission screen will be fading to black to load another. Probably Decay Solo Mission will be doing it better by connecting all missions like other HL games. (works with 25th anniversary update since Valve kept updating for mod support.)