I have to scroll down the list of series that are important to me for one with a clear leader to emerge. Zeldanot a chance. 2D Mariodebated in perpetuity between SMB3 and SMW. StarCraftas with SSBM/SSB4, it really depends on what your priorities are, and how much you treasure oddities in the original game that emerged into competitive techniques. Sid Meier's Civilizationwell, the best is obviously IV, but now there's a whole generation brought up on Civ V that loathes unit stacks and writes off the older entries. Fire Emblemha.
The clearest one I can think of: it's rare to see anybody dispute that the first Viewtiful Joe is the best, but we don't have much of a sample size to draw from (only two main-line gamesthe second one underrateda DS game, and a spin-off multiplayer fighter nobody cares to remember).
After that, as mentioned earlier in the thread, The Thousand-Year Door is the aspirational exemplar for Paper Mario.
Other than that, there isn't much. If you split 2D and 3D Metroid, I think there's a well-defined standard backing for Super and Prime 1, respectively. Then there's 3D Mario, where the Galaxy games stand out as beloved by both the 64/Sunshine and 3DL/3DW crowds, and for good reason. And most players recognize by now that WoW's golden age peaked with Wrath of the Lich King, though that certainly wasn't clear back when the expansion was active, and grumbling about quality-of-life concessions to casual players was as commonplace as it is now. (People's opinions of WoW will always depend on when they were themselves most committed to the game.)
When Mario Kart 8 Deluxe comes out, it stands a good chance of solidifying a consensus, as MK8's Battle Mode was really the only serious obstacle to the game's universal consideration as the best in the series, even if it lacked certain features or modes that distinguished earlier games like MKDS or Double Dash.