These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Anticlimax Boss: The final boss, which is the Big Bad piloting a robot and two TOZ systems. She will use them to steal your weapon, but she isn't able to use the stolen weapon very well. If you have the G-Beam powered up at max, it shouldn't take long at all. Even better, if you have one of the game-breaking secret weapons, the boss won't even be able to copy it correctly and be stuck with Vulcan, making it even more of a cakewalk.
Game Breaker: A certain set of weapons, including the Tektite Blaster (T-Braster, similar to the Hunter from Thunder Force III except stronger), had unique conditions to acquire, some of which are seemingly arbitrary. They were only fired from the TOZ System, could not be leveled up, and were lost at the end of the stage (and you got the Vulcan back - at minimum power). These weapons make the Giga Beam (G-Beam) seem weak in comparison. They could also be obtained randomly in Stage 8.
That One Boss: The boss of the sixth stage, a Humongous Mecha Amazon with a sword and shield. You could only hit her when her shield was down for a second. Furthermore, she had a Spread Shot consisting of three hard-to-avoid large projectiles, said attack was used when her shield was down, and the projectiles were NOT blockable with your TOZ system.
The boss of the seventh level, which is the core of Gulfer's HQ. If you position your ship in the right place, NONE of its attacks will be able to hit your ship! Of course, this comes after the first 6 bosses, including that female gladiator robot...