
The boss of stage 1 of R-Type is one of the most famous of videogame bosses. I knew about it for years before I played the game. It was used in advertisements for the Turbographx 16 (maybe I could scan one later), and it immediately caught my eye.
It's obviously inspired by Aliens, but it adds its own unique touches: The floating eyeballs, the visible circuits.

This is the first boss of Gate of Thunder. It's some sort of space ship. The thing is so damn generic, you could look at it now, and not be able to identify it five minutes later (say, pick it out from other mechanical ship bosses from other games, or from Gate of Thunder).
I can't say that it has any unique features.

This is the boss of stage 2 of R-Type. It's very different from the boss of stage 1, in look and in the way that it's fought. If the stage 1 boss was inspired by Aliens, this is all original. It also is even kind of subversive, with its reproductive symbolism.
I apologize for the blurriness of some of these R-Type screen shots. It's the nature of our tv card when taking pictures of moving objects.

This is the boss of stage 2 of Gate of Thunder. It's ... yet another generic space ship.
R-Type has diverse stages that are not just shooter archetypes. It took risks with weird themes.

This "cartesian spore" stage is something that I was tempted to say hasn't been done before or since (even by the R-Type series). That's not completely true, I suppose. A lot of stages with "shoot-able backgrounds" could be said to be of this type (example, the shoot-able cabbage in that vertical tunnel towards the end of Super C). It still seems unusual. One thing that's particularly unique about the way R-Type approaches this is that not only can the spores be destroyed, but enemies also build them - the growth is both ways.

This "microchip" style background from stage 6 is strange. (The stage in general is strange, too)

It also has some organic stages, like this one which looks like it could be filled with villi. I also believe that this boss inspired the Argus in the Zelda series.
Now let's look at the variety in Gate of Thunder.

Stage 2, a generic mechanical base.

Stage 4, a generic mechanical base.

Stage 6, a generic mechanical base.

Stage 7, a generic mechanical base.
Pretty much every stage is a mechanical base, or eventually moves into a mechanical base, or isn't a mechanical base but looks like one anyway. The single exception is stage 5, which admittedly looks nice, definitely the best looking stage in the game:

One stage that isn't a base but still has parts that look like it is stage 1:

This is a stage that has you flying under a giant space battleship. Hmm, a stage that is mostly a giant space battle ship... It's impossible to see something like that and not think of R-Type's third stage, which famously (it's even mentioned in EGM's GOAT article) introduced the idea of a stage that's a single giant battleship.
The Gate of Thunder battle ship is boring and rectangular. (Like I said, if you didn't notice the fin in that image, it could look like just another base).

The R-Type battleship is interesting, detailed, and rounded.
One common shooter convention is the "wall boss". Gate of Thunder uses a wall boss as its final boss.

The thing about this wall boss is, what is it? Why is it there? What is its purpose. Well, it's a wall boss in a videogame shooter. That's it.

R-Type also has something like a wall boss. But it has a particular function, and its form follows that function. It's a trash compactor. The floor of the room is filled with junked enemies, and the garbage shutes above dropped junked enemies on top of you.
The R-Type boss is specific; the Gate of Thunder boss is generic.
