Yu Gi Oh! 5Ds (meaning "5 Dragons") was the 2008 follow up to Yu Gi Oh! GX, and was based on the manga of the same name.
Running for 154 episodes (although not all of them were dubbed for western release), 5Ds marked an, albeit unsuccessful, attempt to make the series take on a more serious tone, this time round being aimed at the older teen/young adult market, this is fairly evident throughout the first three series (episodes #1 to #65), however the "seriousness" was toned down somewhat afterwards.
Set roughly 10 to 20 years after the events of Yu Gi Oh! GX, most of the series' action takes place in and around "New Domino City", a new technologically advanced utopia built on the remains of the original Domino city (as seen in the original Yu Gi Oh! anime) which is powered by a mysterious power source known as "Ener-D". However, all is not good in paradise, as for the most part, the society of New Domino City is a very elitist one, with "undesirables" being banished to a run down area of the city named "satellite", which is located on an island in New Domino's bay, and once you set foot there, you arent legally allowed to leave (although on rare occasions, exceptions to this rule are made, so long as the rich people see some advantage in it for themselves,which doesnt happen often).
In this future time, the power source "Ener-D", or "Duel energy" as it is sometimes called, has been discovered to be a plentiful source of clean, cheap energy, so much so that it literally powers everything in both New Domino and Satellite. Ener-D is is produced by collecting and harnessing the power generated by people both watching and participating in Duel monsters competition, the more exciting the duel, the more Ener-D is created.
This has led to the invention of a new and more risky type of dueling known as the "Turbo Duel", in which participants ride on Ener-D powered motorcycles (called "Duel Runners") around increasingly dangerous courses, all whilst playing a game of Duel Monsters.
Yuusei Fudo is a resident of Satellite, and the son of one of the scientists who first discovered the properties of Ener-D. Yuusei is a tough street smart kid, and a fairly good duelist, who aspires to leave Satellite behind and make a life for himself in New Domino, however circumstances conspire against him, most notably the fact that residents of Satellite are not allowed to leave the island.
Yuusei manages to get off the island, and eventually runs across a former friend turned enemy, but he also learns that he is one of the fabled "Dark Signers", five individuals descended from an ancient people who are destined to use the five sacred dragons to save the world from evil.
Initially the series is a very dry watch, with the overall message highlighting the every day struggles of the disadvantaged to overcome their lot in life and make something better for themselves, but from about series 2 onwards, the tone of the series returns to the fantasy/adventure type storytelling commonly associated with the previous series, with bad guys showing up and trying to take over/destroy the world with their various evil plans etc.
The series was heavily critisised for the invention of "Turbo Duels", which make very little sense, however the series did see the introduction of the "Synchro summon" game mechanic, which changed the strategic options available to players in the real life card game as well as characters within the series (although like previous series, many cards shown on screen and their effects are somewhat exaggerated, or just completely different to how they behave in real life)
I didn't enjoy the series that much, its attempt to darken the storylines spectacularly backfired as storylines became difficult to follow, or just plain boring. None of the characters were particularly interesting, in fact, other than Yuusei himself, I couldnt tell you any of the other characters names, simply because none of them really mattered much.
I would have to say that of all the five (at the time of writing anyway) Yu Gi Oh anime series', 5Ds is most definitely the weakest and least memorable, lacking the epic storyline of the original series, or the fun factor of GX.