* GeniusBonus: In the first game, O2-Joy's theme music is a minor-key version of the Ode To Joy.
* SurprisinglyImprovedSequel: Aside from well-designed and fun boss battles (especially the last one), the first game is a decent if unremarkable side-scroller. The sequel is a top-notch ActionGame with incredible pace.
* ThatOneBoss: Omega Darn from the first game is utter chaos in boss form, with the player constantly having to switch between their different forms. And it's very easy to accidentally switch when you didn't mean to and take a barrage of lasers or homing missiles right in the face before you can switch back and dodge. Not to mention that eventually the boss adds a screen-filling attack to its arsenal that deals massive damage, and the only way to avoid it is to hit him with a missile before it activates or desperately throw yourself against another, less-damaging projectile to take advantage of your MercyInvincibility.