Although the name doesn't indicate as much, Tron Bonne is the second game in the Mega Man Legends series, having been released in 2000. It serves as a prequel to 1998's Mega Man Legends and has become one of the rarest PS1 games--it's not uncommon to see it sold for $250-$300 or more on eBay.
An ESRB rating for the game was recently discovered by Siliconera with its platforms listed as PS3, PSP, and PS Vita--suggesting a PS1 Classics re-release. Sure enough, the game was released not long after as just that, and you can now buy it for a fraction of the price you would have paid just days ago.
Unfortunately, Tron Bonne is the only Legends game currently available on PSN. If this serves as your entry point to the spin-off series, you'll be further disappointed by the news that Capcom canceled Mega Man Legends 3 in 2011.
PS1 Classics still aren't playable on PS4, so you'll be limited to one of the three aforementioned systems or PlayStation TV if you pick this up. Still, it's great news to see more and more rare games made widely available through services like PSN and Virtual Console.