Various video edits, additional characters added, OPs and EDs changed, and sex changes/splits.
The original series was actually brought over twice as 'The Battle of the Planets' and then later redubbed with a differnt stroyline (but still inaccurate to the oriignal) as 'G-Force'. Gatchaman II and Gatchaman F were combined to make 'Eagle Riders'.
NOTE: ADV is releasing the orignal Gatchaman uncut on DVD.
DETAILED REPORT

NOTE: Due to the age of this show, many details are done from memory and from various sources. Not all have been personally verified by the reviewers.
Jim Lazar (Webmaster/animeprime.com)
Mike Breen (Gatchaman '94 OVA information)
Angela Porter (additonal info on TV series)

Battle of the Planets and G-Force (Gatchaman TV series): Unknown
Eagle Riders (Gathcaman II and F TV series): Saban
Gatchaman '94 OVA: Urban Vision
Orignal Gatchaman uncut: ADV

Gatchaman TV series: As originally broadcast on Japanese television
Gathcaman II and F TV series: As originally broadcast on Japanese television
Gatchaman '94 OVA: As released on Japanese home video
Original Gatchaman uncut: As originally broadcast on Japanese television

Battle of the Planets & G-Force: Major impact on original story and characters. Changing the mutant into brother and sister and adding completely new characters changed this story at a fundamental level. (Although it has been a LONG time since I've seen this show, so my source's and my own memories may be hazy).

Eagle Riders:Various changes to the story and plot.

Gatchaman '94 OVA: The English sub did not alter the story/plot, but the English dub changes did alter the overall story and made it much more childish than the original was intended to be.

Original Gatchaman uncut: Not edits are expected in this new uncut release.

Battle of the Planets and G-Force were both derived from the original Gatchaman series.

Battle of the Planets: Various edits for time, content, and story changes were made to the video. One major change is the inclusion of entirely new characters (such as 7-Zark-7 and 1-Rover-1 which were added as filler for plot exposition.

G-Force: Various edits for time, content, and story changes were made to the video.

Eagle Riders: Various edits for time, content, and story changes were made to the video. Eagle Riders was derived from the 2 follow-up Gatchaman TV series, Gatchaman II
and Gatchaman F.

Gatchaman '94 OVA: No video changes reported.

All TV series: No English subtitle versions available.

Gatchaman '94 OVA (information from Mile Breen):

• All references to the ship being the "God Phoenix" were removed. Even in
  the sub, it's called the Phoenix.
• Aside from the conspicuously missing "God" from the ship name, The sub
  translation is a bit too literal at times. "Soosai X-sama" was translated
  as "President X," for example. But they don't actually change any of the plot

I only saw the first volume before I returned it in disgust and exchanged
it for the subbed version, so a lot of this comes from memory. There some
other stuff that I actually got off of UV's web site. Interestingly, they
swap the names (click on "Jimmy" and they tell you about "Jimpei").

• No actual footage was cut (with the exception of the music video on volume
  3, which was missing from the sub but included on the dub), so at least the
  possibility of a bilingual DVD is there.
• First off, they changed the names. They kept Ken and Joe (probably
  because they were "American"), but changed Jimpei to "Jimmy," Jun to
  "June," and Ryo to (this is rich) "Rocky." Berg Katze was changed to
  "Solaris" (allegedly so that UV wouldn't offend Steve Katzenberg), and
  Soosai X was changed to something like "Lord Zartek" or something equally
  as Power-rangerish.
• The subplot about Jun and Ken's attraction to each other was completely
  removed and replaced by completely different dialogue. When the team
  splits up to take out the enemy from different approaches, Ken takes Jun
  with him. In the original, Jimpei says "Way to go, sis," and Jun responds
  by bonking him on the head and saying, "Why you," or "Cut it out," or
  something like that. In the dub, Jimpei asks Jun to get him a
  souvenir. Jun *still* responds with the bonk and the "Cut it out."
• Jimpei's "bird form" in the original was a swallow. In the dub, he's a
  falcon.
• Galactor, instead of being a private, human terrorist group led by a
  single alien (Soosai X), were now *all* aliens, which would significantly
  alter later plot developments, as X's plan was to bring his chosen few to
  space with him while the Earth was "cleansed."
• In the original, Joe's parents were Galactor agents who were assassinated
  for breaking with the organization. In the dub, they *added* a subplot
  about Joe being a Galactor alien. Apparently they made a big deal out of
  it, judging from the box copy of the third volume which went on and on
  about how Joe's "alien blood."
• The Turtle King robot was renamed the "Dragon King" (even though it's
  clearly a turtle).
• The Jupiter Ninjas in the dub are androids (aren't we a little old to be
  fooled by the android trick?) called the "Jupiter Death Brigade."
• The Blackbird Ninjas are now called the "Blackbird Battalion." But at
  least they're human.
• All references to the ship being the "God Phoenix" were removed. Even in
  the sub, it's called the Phoenix.
• And in general, the plot was dumbed down and kiddified.
• Aside from the conspicuously missing "God" from the ship name, The sub
  translation is a bit too literal at times. "Soosai X-sama" was translated
  as "President X," for example. But they don't actually change any of the plot.

Ken Washio = Mark
Joe Asakura = Jason
Jun = Princess
Jinpei = Keyop
Ryu Nakanishi = Tiny Harper
Nambu = Chief Anderson
Berg Katse = Zoltar
Sosai X = Great Spirit / Luminous One

Ken Washio = Ace Goodheart
Joe Asakura = Dirk Daring
Jun = Agatha June
Jinpei = Peewee
Ryu Nakanishi = Hooty Hootowl
Nambu = Dr Benjamin Brighthead
Berg Katse = Galactor
Sosai X = Computor

Ken Washio = Hunter Harris
Joe Asakura = Joe Thax
Jun = Kelly Jenar
Jinpei = Mickey Dugan
Ryu Nakanishi = Ollie Keeawanal
Nambu = Dr Thaddaeus Keane
Dr Pandora = Dr Aikens
Gel Sadra = Mallanox
Sosai X = Cybercon

• Currently the only way to get the complete and uncut Gatchaman II and Gatchaman F is by obtaining an import version from Japan (should be available on assorted home video formats from various sources).
• ADV is releasing the orignal Gatchaman TV series uncut on DVD.