You can check out the full catalogue here.As you'll probably notice a lot of the new additions come from the CD-ROM era of DOS gaming, where games shipped on 700MB optical discs containing all manner of recorded music and full-motion video (or FMV). As per the update, the team notes that internet speeds of today mean that downloading and storing all this data in browser memory is possible but can also be a problem. With goal of this archive being preservation no doubt this will only improve over time.
CD-ROMs were a boon to the early-to-late 1990s, allowing games to have audio and video like never before. Depending on the tricks used, you got full-motion video (FMV), the playing of CD audio tracks for background music, and levels and variation of content for the games far beyond what floppy disks could ever hope. But it was also a very large amount of data (up to 700 megabytes per CD) and its one thing to have the data sitting on a plastic disc in a local machine, and yet another to have a network connection pull the entire contents of the CD-ROM into memory and hold it there as a virtual file resources. This is going to be an enormous lean on the vast majority of Internet users out there downloading multi-hundred-megabyte files into memory and then keeping them there, and then losing it all when the browser window closes. Network speeds will improve over time, but this is probably the biggest show-stopper of them all for many folks.
If you find yourself loading up one of these games and facing down a hundred-megabyte download, consider one of the smaller games instead, unless its a title you really, really want to try out. Maybe in a few years well look back at cable-modem speeds and laugh at the crawling, but for now, theyre pretty significant.