Note that the later DOS / PC version of this game was somewhat different. The graphics were more advanced and rendered in a full range of colors for the time, as were the more complex world background paintings. Also, the cloaking device was not integrated into the tank and did not end the game or destroy the tank when it ended. Each world also was guarded by a boss that had to be defeated before the warp-link to the next level would appear. Most of the bosses were not particularly complicated compared to the sequel (Nova 9), but they presented a reasonable challenge for the time. The power-up system also worked differently. By killing 3 of specific enemy types, you would get a power-up dropped, which would then activate when you touched it; different enemies produced different power-ups following this system. Finally, the game had a "Continue" feature, vs simply ending when the tank was destroyed. Other differences may have existed between the enemy types and behaviors; the same applies to power-ups.