I managed to track down the full first episode of Transformers: Prime's Japanese version. You can watch it below, and you can hear what I have to say about it after the break.
Obviously, the first thing I paid attention to was the voice acting.
All of the Transformers shout "TRANSFORM!" when changing modes, and "ARMS UP!" when deploying their weapons.
Cliffjumper was far from being manly enough. We get the Rock, and Japan gets a hyperactive guy who enjoys singing about himself. Luckily, Cliffjumper's voice acting wasn't a problem for very long, if you know what I mean. XD
Arcee's voice is okay. The pitch is good, but the tone gives me the impression of a teenage girl. Also, she seems to enjoy saying "saiyaku"...
Optimus Prime seems too excitable, I feel that he should have been more calm and collected. Of course, I'm rather hard to please when it comes to Optimus. I don't think I could have been satisfied with his voice unless they taught Peter Cullen how to speak Japanese. XD
Ratchet's voice is one of the best, in my opinion. He does sound a bit flamboyant, but not too extreme.
Starscream's voice is REALLY over-the-top. He sounds FABULOUS to the extreme, to the point of shouting "HOOOOO!" like Hard Gay. (If you don't know who Hard Gay is, he's a Japanese TV star of sorts. Disturbingly hilarious.) ...Anyway, Starscream's voice made me laugh way harder than necessary.
Bulkhead's voice is great, possibly better than Ratchet's. I can't think of anything they could improve on.
Jack's voice is pretty good, though he plays up his emotions a bit more than the American voice actor. He sounded a bit too... excited when he first saw Arcee... as if it wasn't bad enough that he immediately proceeds to feel her up...
Raf's voice is also pretty good, didn't really stand out one way or the other.
Miko is okay, but she doesn't sound quite hyper enough.
Megatron doesn't sound nearly sinister enough...
Oh, and Bumblebee and Soundwave are PERFECT. The localization team did an AMAZING job picking voice actors for these guys, lol. XD
As for content that was added, there's the new opening and ending sequences, ka-ching wipes, the pop idol group skit, and the Arms Microns segment.
For anyone who doesn't know, ka-ching wipes are the screens that transition to and from the one commercial block that half-hour time slots have in Japan. Prime's ka-ching wipes consist of characters saying their names, then shouting "TRANSFORM!" while the screen shows statistics regarding things like their strength and speed. Episode one used Optimus and Arcee.
The bit with the pop idols just felt really awkward to me... Also, it kind of doubled as a toy commercial...
The Arms Microns segment is the first of one planned for every episode. It's a short segment that revolves around the Arms Microns, smaller Transformers that are included with the toys in Japan. Instead of vehicle modes, they have weapon modes, and are intended to be attached to the normal-sized figures.
To make room for the two new segments, some original content was removed. This includes some of the more graphic parts of Cliffjumper's death scene, such as the moment when Starscream slowly pulled his hand back out of Cliffjumper's chest. This was likely done for censorship reasons as well, as Prime aired at 8:00AM in Japan, not 8:30PM. Another scene that they cut was Raf playing with the remote controlled car. However, they still showed the awkward scene with Bumblebee stepping on it, making it seem like it came out of nowhere.
Despite some of the weirdness, and possibly BECAUSE of some of the weirdness, I enjoyed the episode. The content of the episode itself doesn't seem to stray too far from the original, and most of the voice acting was either well done, or hilarious. XD
Welcome to the convoy, Japanese fans.