Bad Export for You: While both games on the next-gen consoles have been released overseas, the show tunes from various Gundam series (Ex. Anime Ja Nai, Rhythm Emotion) are only available in the Japanese versions. Also, the export versions of the second game are not dual-audio like the first and third games. And the 4th game is download-only in the US.
Although this is justified since all these songs would require licensing fees and with all the shows in the game the fees wouldn't be cheap.
No Export for You: Dynasty Warriors: Gundam: Special/Gundam Musou Special for PS2 which introduced Musha Gundam MK II was only released in Japan. Not really a loss in any way since unlike most of the entries on that page, pretty much every improvement and addition was shunted to 2, along with 2's base improvements.
What however is a no export for you is the Vita version for Gundam Reborn in the west as well as losing a disc-based release in the US (both won't get the Vita version but the disc-based version will be available in Europe).
The Other Darrin: The English versions of the games were unable to obtain the services of several voice actors who worked on the various Gundam anime series, and thus had to recast some of the roles. For example, Mark Gatha (Domon) retired from voice acting to become a doctor, and Mark Hildreth (Heero) was for some reason "never called back" to voice Heero. Travis Milne, who voices Kamille in the first two games, is replaced by James Beach because the former is involved in Rookie Blue, which is a TV series based in Toronto.
Talking to Himself: In the third game, Brian Drummond plays both Heero Yuy and Zechs Merquise/Milliardo Peacecraft. To Drummond's credit, the two sound almost nothing alike, although he very rarely tends to slip into Milliardo's gravelly voice while speaking as Heero, most often when saying Heero's Catch Phrase. And it's not that he can't do it, (he does so quite well, in fact), it's just the bizarre-ness of him playing Heero after spending the last decade playing Zechs in the Wing anime and various video games.
Also in Japanese, we have the most definitely intentional case of Shuichi Ikeda as Char Aznable and Full Frontal. However, this shockingly didn't make it into the English language version, as even though Frontal is stated to have a voice that cannot be distinguished from Char's, he's voiced by Jonathon Love as opposed to Michael Kopsa. It still is played straight, though, as Love also plays Paptimas Scirocco (not that you'd be able to tell if you weren't listening carefully enough).
Kamille is often seen in Gyunei's Jagd Doga, possibly a Shout-Out to the persistent rumor that Gyunei was created as an Expy of Kamille after Tomino rejected the idea of Kamille showing up in Char's Counterattack fighting for Char after being put through some questionable brain surgery.