Turning back the clock to 1985, when Gradius first started out as a stand alone arcade game. It looked like a typical side scrolling shooter at first, but upon playing it, was much more than that. Gradius had a unique type of power up menu system, such as option, laser, missile, and force field. The menu was accessed by obtaining pill type icons when you destroy certain types of ships. The release of Gradius on the Nintendo 8-bit system also help give birth to the original Konami code that was used to get full fire power in Gradius, and as it also gave 30 lives in Contra. As time went on, the sequel to Gradius, simply called Gradius II, mostly shined on the arcade format, as others didn't live up to the game graphic wise. There would also be greater improvements when Gradius 3 was developed, but there were also issues with slowdown.
If you remember the bubble stage, Gradius 3 suffered horribly from a slow CPU and made the game less playable for some, although it's been said that the slow down issue made it easier to get through it all. Gradius IV didn't even see the light of day until exactly 10 years later, and it also lacked the weapon editing function of past Gradius games, however it did have a greater amount of weaponry to use within the game itself. It made Gradius have a new turning point in its history, something new to the series. Gradius V didn't make the scene until a few years later when the Playstation 2 was at its height in popularity, and thus introduced a new 3D type setting environment, although much of the game flow had stayed within a 2D realm, as Gradius has always shined in.
To this day there hasn't been a follow up to Gradius V, but between its birth back in 1985 up until now, there have been other Gradius adventures, such as the Game Boy Advance and other lesser systems. It was basically spinoffs between now and then that took after the Gradius series. Games like Salamander, or some of you may know it by another name, which is LifeForce. Salamander was a different twist to Gradius, in that it had both horizontal and vertical type stages added to it, that was likely a first in shoot em up history. The weapon upgrade system was almost identical to the Gradius series, as it had the same options, except Salamander had a few others, such as Ripple.
The last somewhat of a spinoff took place with the Parodius series. I say "series" because there was more than one of them, and it took on a whole new meaning in terms of how Gradius games have always looked. Parodius had more of a cartoon type graphic setting that seemed weird by comparison. The weapon upgrade system also was slightly different from Gradius, but was for the most part the same basic concept. Nemesis was a spinoff that marked the first time in Gradius history that a portable hand held version of Gradius could now be played, and also borrowed elements from previous Gradius games to boot.
Where is the Gradius game franchise headed to nowadays? No one really knows except for Konami games development, and a new Gradius game hasn't really been produced since the birth of Gradius V back in 2004, almost a decade ago. Only lesser systems like Mobile devices and Nintendo's WiiWare system have seen a rebirth of Gradius, and it seems in the past few years Gradius has yet to make a comeback. I predict that given the time, Konami will see to it's resurrection.