Only two series come to mind that exploit their longstanding success from the past, today: Shining Force and Phantasy Star. Oddly enough, they both come from Sega. Shining Force has gone from a fun strategy RPG series to an average action RPG series. Then, Phantasy Star went from a classic menu turn-based RPG series to a carbon-copy MMO series, IMO anyways. But yeah, Losfer mentioned these already, I have to concur.
I agree as well, those are the two that I will always remember for their fall from greatness. Both (arguably) were right with the other candidates for pinnacles of their original genres, atleast to me, and now both are pure piles of you know what...
Yeah, I still can't believe they ditched probably the coolest character in Grandia III, the mother.
fall from greatness? maybe i just dont understand since phantasy star online was my introduction to the series but the only of the older games i can bring myself to play,and enjoy is phantasy star 4. perhaps it has more to do with the fact that i value gameplay over story. sorry but the gameplay of ps 1-3 is shit. phantasy star 4 stands up very well to the test of time wich is why i wish sega would release the phantasy star generations here in the hopes that they would be the old games with updated graphics and ps4'ish gameplay. like them or not the online phantasy star's are no where near worthy of being mentioned in the same breath as the recent shining force games.