Hmmm...
Zach's Almighty Verdicts
Majora's Mask shall not be considered a "new" Zelda game, as it uses the exact same engine as Ocarina of Time, was released just over a year later, and isn't so much a sequel as an Alice in Wonderland sidestory.
Mega Man Legends is to be considered the first game in a new franchise, and thus not a true Mega Man game. We do not consider Mega Man X to be a part of the Mega Man proper lineage, nor do we give such heed to Mega Man Zero, Mega Man ZX, Mega Man Battle Network...etc.
Metroid Prime Hunters shall be considered a sidestory to the main Metroid Prime canon, not an MP game proper. Also, the Quake gameplay differentiates it from the main games to a great degree.
Umbrella Chronicles shall be considered the first game in a new RE franchise. Its railgun shooter gameplay differentiates itself from the main series. Additionally, it serves as a "summary" of the RE story from RE0 to RE3.
Four Swords is a bizarre sidestory to the proper Zelda timeline. There is virtually no crossover (except for Ganon's unexplained occurance in the GC game), and no mention of Vaati or the Four Sword is made in the main gameline. Thus, Four Swords represents its own series.
Circle of the Moon is not considered canonical by Igarashi, but its gameplay formula is so similar to the seminal PS1 classic, Symphony of the Night, that its place within the Castlevania series proper cannot be ignored. There are currently FIVE Castlevania series:
1) NES/SNES/Genesis sidescrollers featuring linear level design.
2) N64 forays into the 3D realm. Their pedegree is not seen in the recent PS2 Castlevania games.
3) PS1/DS sidescrollers featuring what's come to be known as a "Metroid-vania" level design and a focus on magic, branching plot paths, etc.
4) PS2 forays into the 3D realm. Neither one succeeded.
5) The upcoming Wii fighting game.
I have spoken.