Not really. While the Geomon games vary greatly in gameplay style, the Zelda formula has probably been the dominant gameplay style for the series. And there are even two other 3D Zelda style games (The PS2 game and one of the PS1 games).
The first two Famicom games have the Double Dragon style level based beat-em-up town thing.
No, while you do walk around and hit people, the games have nonlinear stages you wander around, a money system, etc. It's much more like the first SNES game but without the platformer levels than a Double Dragon. Double Dragon doesn't have exploration and grinding, after all, while the first Famicom Goemon game very much does!
And the first two SNES games follow this and add platforming stages to it. But there were also the two Famicom RPGs.
After Ganbare Goemon 2 on SNES, the Goemon series largely went full-Zelda for more than half of the series entries. Ganbare Goemon 3 is basically a full-on Zelda game with platforming stages as the dungeons.
More than half of the Game Boy games (Kurofune To no Nazo, and Playstation games (Goemon Uchu Kaizoku Akogingu, Kuru nara Koi! Ayashige Ikka no Kuroi Kage) also follow this formula, as does the DS game (except it doesn't even have the platforming bits basically).
Mostly true, but still the first N64 game was quite original, considering that it released a year before OoT and thus is not an OoT clone, but a predecessor...
I would also add that the 3d Playstation game (Kurunarakoi) is not really much like a Zelda game at all; it's mostly a 3d platform-action game, with hack-and-slash combat and on-rails 3d platforming. There are towns of course, but still, it's no N64 MNSG. I haven't played the PS2 game but it is supposed to be more like that, but without any of the comedy that helped make the series great. (Oh yeah, and the 'Zelda-ish' GB game, the one that we did get here, is no good and is one of the worst Goemon games. But it IS a top-down action-adventure game, so it does count.).
Also, while it is true that Goemon 3 and Space Pirate Akoking have Zelda-style overworlds, and the first SNES Goemon also has that big overworld element, the 2d platformer levels make up significant amounts of all three games, Akoking perhaps more so than the others, so they aren't just Zelda-ish games, they are also platformers.
There are also almost as many traditional RPG Goemon games as there are SNES Goemon 2 style: Famicom (Goemon Gaiden 1 and 2) Game Boy (Tenguto no Gyuakushu, Mononoke Dochu Tobidase Nabe-Bugyo).
The first three of these are indeed menu-based RPGs, but isn't that last one a GBC version of the Goemon Mononoke Sugoroku game for the N64? If the GBC game is like the N64 game, while there is sort of RPG-ish combat, I wouldn't call the game an RPG. It's a boardgame with a weird card/RPG-style battle system.
Goemon is definitely a weird series, it's very interesting how many different gameplay styles they used. Awesome, awesome series, it's sad Konami let it die...
