In stable, you would see the user's cursor continue to move after the last hitobject until the results screen was displayed. Until not in lazer, it would cut out precisely at the last object, which didn't feel good.
In stable, if a hit circle is not hit on time it fades out until it becomes impossible to hit and registers as a miss. In lazer, a hit circle doesn't start to fade out until it's already registered as a miss. This change mathces the classic feel of note fade.
In stable, the storyboard filename is fixed (reference). In lazer, we were always looking for the first .osb in the database. In the case a beatmap archive housed more than one .osb files, this may load the incorrect one.
With the release of the lazer subserver there's been an influx of people trying it out, and one of the biggest concerns for taiko players is that the 4:3 aspect ratio isn't supported in lazer without the classic mod.
A common user request is to \"make lazer share a beatmaps directory with stable\". This finally realises that goal when both games are on the same drive, using \"hard links\". You can find more details about how this works at the explanatory wiki page.
This retrofits a minimal subset of scoring data that is required by lazer in order to properly show scores to the end of .osr files. This leaves the files backwards compatible with osu-stable should you choose to import a lazer replay into it, and also perhaps the path for us to potentially show lazer scores in stable 59ce067264