Ah, the Metanet Hunter Series. It's quite the interesting one, centered around a specialized robot called a Kinzo. Each one's filled with orb obliterating action, and serves its purpose quite well.
Originally started with Metanet Hunter 1, it took the form of a Gameboy game, and featured about 6 different worlds. There is a way to indeed unlock a Plus Mode, with 4 extra worlds to explore!
It received a sequel by the name of Metanet Hunter REMIX almost a year afterwards, which adds shooting, unique armor upgrades, and tons of other stuff. It features 8 worlds instead of the standard 6. Originally, it was intended to receive a 1.1 update, adding a bunch of new game modes. It was also intended to have a Fantasy Game, were the game to become popular.
Shortly after, Metanet Hunter SE was introduced as an essentially redesigned Metanet Hunter 1, with brand new art, some new music, and featuring a highly experimental engine! It's a testbed for something big in the future. It was entered for GBJam 3, but it ended up flopping horribly.
To this day, the series remains rather obscure. With a first game, sequel to the first game, and highly enhanced first game, there could potentially be a sequel to Metanet Hunter REMIX in the future, but that's unconfirmed as of yet.
The one that started it all! It eventually got redesigned and refurbished as Metanet Hunter SE.
The best Metanet Hunter! And it's free!
The second entry in the Metanet Hunter series! Featuring an even better soundtrack, remixed graphics, remixed level design, and it's now 150% RADICAL!