If you liked the Planzet anime, the Anime-Planet community thinks you'd like:
In the year 2025, ten billion people inhabit Earth. Science and technology have evolved immensely and people have begun to transform other planets to be able to sustain life. When a spaceship on a return trip from Mars carrying a large cocoon-like object explodes and crashes in Tokyo, it unleashes a seemingly unstoppable monster, Negadon, capable of destroying the world. Ryuichi Narasaki, a robot engineer haunted by his daughter's death caused by one of his creations, and his giant robot are Earth’s only hope. But after giving up robotics ten years ago, can Ryuichi and his robot defeat the monster from Mars and save all of humanity?
Negadon and Planzet are both CGI anime about people who defend Earth from an otherworldly being. Both anime feature mechs and have somewhat simular feel. Neither anime are all that great (though I personally liked Planzet a little bit more than Negadon); still, if you liked one you may want to check out the other.
These two anime have a surprisingly similar feel, production-wise, which makes sense as they share the same director. Both are fully CGI titles with a fairly shallow, formulaic sci fi plot that have a similar 'filming' style.
In the far future, the world lives under the guidance of Olympus – a utopia built after the end of a global war that decimated over half the world’s population. Mankind lives beside both cyborgs and bioroids, a breed of genetically-engineered humans who don’t feel negative emotions. Deunan and Briareous continue to fight for the Olympus task force E.S.W.A.T., but after Briareous is injured in a mission involving a terrorist attack, Deunan is forced to partner with Tereus: a prototype combat bioroid whose genetic makeup was taken from Briareous. Together, the three must try to unravel an insidious terrorist plot and save Olympus once more.
Mecha. CGI. Science fiction cliches. Not particularly memorable plotting or characterisation. You want to just while away some time with stuff being shot at and things looking pretty CGI, either Ex Machina (a sequel to the Appleseed Movie, so seeing the first is recommended but not required) or Planzet is perfectly fine.
In a world where mankind is at the brink of destruction, one lone scientist has concocted the means to save it: bioroids. These artificial humans coexist with humans in the city of Olympus, under the watchful eye of the supercomputer Gaia -- to stabilize society. The military strongly opposes their use, however, and the elite soldier Deunan may hold the key to saving both the human race and the lives of the bioroids. Teamed up with an old friend, Briareos, Deunan must race against the clock to discover the secret of the Appleseed before countless lives are tragically lost...
Appleseed's CGI may have aged while Planzet's is state of the art (...relatively speaking, for anime) but both are basically anime that are big on CGI sci-fi action and a trifle lighter on story elements. If you watched one for this, the other may amuse.
In the early 21st century, insectoid organisms are invading the galaxy, searching for new stars to house their young. Mankind's only defense lies with space cadets such as Takaya Noriko, daughter of a celebrated admiral killed in battle, and Amano Kazumi, the top of her class. With their skill and the power of the mecha known as GunBuster, the girls must help fight to protect the galaxy from total annihilation...
Gunbuster deals with a similar idea - people must battle invaders to protect humanity, there's plenty of sacrifice and hardship along the way. The tone isn't the same, but Gunbuster - with the exception of the first two stupidly ecchi episodes - does it right and is one of the most epic anime I've seen. Try it out.