The interesting thing about the SNES is how many times people just made the same games, over and over.
There is no appreciable difference between Imperium and any other vertical shoot-em-up. Enemies fly down in patterns, occasionally firing bullets; you must avoid their bullets and hit them with your massive stream of bullets, which are fired by holding down a button – a button which might as well toggle on/off, or even better, just constantly fire by default.
What was the point of making this game? I can only guess it was entirely commercially motivated. The genre was fairly popular, and people would buy their game. I can’t imagine that anyone had a burning passion to make a tremendously generic vertical shmup with giant robots that made absolutely no gameplay changes and was in fact more generic than its predecessors, somehow.
This happened a lot with this system, even more than it happens now, although you can easily point (and laugh) at the endless series of WW2 first person shooter games that have been coming out lately.
But, back to my point: it seems like not even one of the developers for this game had a creative urge. They did not come up with anything exciting or original to put in the game; not a single gameplay element exists in the game that is not completely derivative. You can shoot, you can move around, you can use a “bomb” to do damage to all enemies on screen. Enemies are really standard and you must shoot them until they die.
When I play this game I feel like I am babysitting an unloved child who stares at the television all day and absently scratches at its groin. Its unblinking gaze is disturbing not because of the unknown intentions that lie behind it, but because of the lack thereof; sending it home is a relief.
Just play Ikaruga again.