Lennus series. It got 2 games, and the end of the 2nd game sets up for a 3rd sequel that would take place on planet Raiga, but that sequel never happened. (Also, only the 1st game made it to the US, with the misleading title Paladin's Quest (the main character is a mage, not a paladin).)
Years ago, from the later SNES era all the way until a point during the Nintendo DS era, I would have put the classic mario games on the list. The NES got 3 (assuming you count exactly one of Lost Levels and USA, as Lost Levels is arguably more of an expansion of 1 and USA is completely different mechanically), yet the SNES got 1, and then the classic series just disappeared.
Here's why other games with the Mario title don't really count:
* SMW2: Yoshi's Island: The gameplay is completely different, there's no power-ups, there's something like a health meter that decreases when baby Mario has been knocked away and recovers to a point once you rescue him (instead of the classic approach of losing your power-up or dying if you have none), and egg throwing dominates combat.
* Super Mario RPG: This isn't even the same genre. Again, you don't find power-ups in this game, and combat is turn-based with action commands and is on a separate screen.
* Super Mario 64: This game isn't just a 3D sequel to the series. We, again, have no power-ups that aren't on a timer, no fire flower, no loss of power-up on hit. Instead, we have a health meter, falling damage, and having to come up for air while swimming. Also, Mario can now punch, which really doesn't feel right. This game does not play like a 3D version of the classic forumls would.
(Of course, later New Super Mario Bros. came out, and *finally* we had a new entry into the classic series rather than to a 3D or "RPG" spin-off series.)
