SCRAMBLE / Konami / Arcade
Scramble is a pretty interesting early shooter from Konami that relies on clever layout and play mechanics for a challenge, rather than just throwing shit tons of enemies and projectiles at you and forcing you to memorize a precise sequence of moves in every level.
You pilot a spaceship which is basically just trying to survive a gauntlet of rocket launchers and other defenses as it flies low through mountain passes and trenches for some reason. You can shoot small bullets straight ahead to fend off incoming spacecraft, and drop bombs that arc downward to take out missile launchers and also to explode fuel canisters which (somehow) restore your fuel supply. Get hit once by anything, or run out of fuel (which dwindles pretty fast as you fly about), and it's lights out for your valiant little craft.
The game scrolls through five levels of this, with increasing difficulty, then ends with you needing to bomb a base to complete the game. Once that's done, you return to the start of the game again, but there's slightly more enemies added to the rotation. Continues forever, I guess, or until you deplete your stock of lives.
The Gameboy Advance game Gradius Galaxies listed this game as the first of the Gradius series, although Konami apparently later redacted that. You can see some similarity to Gradius in the use of cavern levels and mix of ground-based enemies and flying enemies, but the gameplay style is really pretty different.
I thought the game was fairly fun to play, but the difficulty starts out pretty high and only gets more relentless as you proceed. After maybe ten or fifteen minutes of play I felt it was getting too hard to be playable any more, unless you're like The Wizard or something. It's also a bit repetitive - terrain and enemies are very samey throughout, giving you not much real incentive to put up with the difficulty.
* Gameplay Video