I'll start off with the Soul Calibur series. Tell me about your percieved brightest entry, be it Pokemon, WCW vs NWO, Tekken, Tales, Final Fantasy, Kingdom Hearts, whatever man! I wanna talk about it!
Soul Calibur II was my entry, and dominated my sword-fighting games until SCIII came out. I actually bought it a year after its release, and it was still better than any other 3D fighting game I've ever played.
SCIII took II's formula and added CREATE YOUR OWN CHARACTER (Create-A-Soul), which was a pretty intense fad amongst Playstation II games.
The creation system shined throughout the whole game. Default character movesets were treated as the highest, and therefore were extremely hard to unlock. To compensate, there were almost 20 unique character movesets to choose from, and from various classes like Dancer, Thief, Ninja, and Knight. I personally enjoyed the Lance Moveset, which took inspiration from Kilik and Siegfried's moves.
As another focus, a completely different mode, a campaign-style mode that functioned as a highly interactive RTS strategy game... it was amazing, held a great story that somewhat incorporated the default characters as side challenges, and allowed for amazing replayability.
Of course, it had an Arcade mode (still pretty good, better than anything else because of the various types of matches). It also had challenges, like pitting you versus a 3-story high colossus or matches that disabled blocking. The tutorial was also excellent.
And if I could harp on it any longer, the customization was intense. Too many ways to make the perfect fighter, very many possible cosplays. Amazing armor with a free-ranging pallete on every single article of clothing, hair, skin, eyes, anything was possible. My favorite characters will never be forgotten, because I still know exactly what they look like. They also had alignments based off of their garments, which gave them an entire range of voiceovers ranging from innocent girls to ambitious soldiers to the most blackhearted of knaves. And as an added bonus, the default characters all had amazing outfits and alts, so their options were pretty wide as well. How about a more adventurous-looking Siegfried with Red hair and true blue Scarf? What if Ivy had purple hair? What if Voldo's skin was a normal color?
Seriously... Soul Calubir III was the fucking best. It's a crying shame it didn't get much attention, or more versions. If it had made it to Xbox those sorry excuses for Sould Calibur games IV and V would never have reached such abysmal levels of boringness. They really dropped the ball after SCIII, but I'll never forget that time where SCIII existed and was the latest in what was then a series of masterpieces.