The title contains three classic 3D Mario games - Super Mario 64 from the Nintendo 64, Super Mario Sunshine originally for the GameCube, and Super Mario Galaxy for the Wii. These are arguably the most significant outings in the franchise, though the collection skips out on Super Mario Galaxy 2, possibly to avoid including two very similar experiences in the same package.
The games will look pretty much how you remember them, and Nintendo hasn't done a lot to improve them. Controls have naturally been tweaked to fit the Switch hardware, the resolution has been increased, and - for Super Mario Sunshine - the games will now run in 16:9 aspect ratio, rather than 4:3 like the originals. Super Mario 64 didn't get upgraded to 16:9, and Super Mario Galaxy was already 16:9 on the Wii, so that remains true here.
The package also includes the soundtracks for each of the games, with each game sorted as its own album. Fans of the music in Mario games will be able to listen to them whenever
Super Mario 3D All-Stars is launching as a limited retail run later this month on September 18, and the digital version will only be available through March 31, 2021, so you'll need to grab it quickly if you're interested.
Update: The original article incorrectly stated that Super Mario 64 had been upgraded to run in the 16:9 aspect ratio. Only Super Mario Sunshine has seen this change, though Super Mario 64 does have higher resolution than the original release.