Kotetsushin Jeeg takes place fifty years after the original and features a new cast of characters—primarily the new main character Kenji Kusanagi, a high school student who becomes Kotetsushin Jeeg to fight the sudden reappearance of "Haniwa Genjin" ("Haniwa Phantom Gods", or clay robots) from the Jamada Empire ruled by Queen Himika. Other characters include Tsubaki Tamashiro (grandaughter of Miwa Uzuki); and Kyou Misumi. Other main characters from the original series also appear.
Decent show, very much a "monster-of-the-week" series. The directors even said themselves that it was basically a simplistic mecha show without too many complications and was made mostly as a sequel/tribute to the original Koutetsu Jeeg. Hard-headed, gung-ho pervert protagonist Kenji gets drafted into service by Build Base after he and his friends are enveloped in a weird black mist. He doesn't particularly mind however, because they give him a sweet chopper that turns into the head of a sweet robot, Koutetsu Jeeg, and tell him to go forth and kick butt with them. The plot is essentially a continuation of the events that took
place in the original Koutetsu Jeeg, and ties in to said events very well towards the end...most of the cast from the original show show up at some point.
There's sort of a love triangle set up in the beginning, but it very quickly dissipates because Kyo is just mysterious to love anyone, apparently. (You find out why later.) Kenji and friend-that-is-a-girl Tsubaki sort of have a love/hate relationship, but it never really develops until the very end in a very awkward and anticlimactic way. Relationships in this series are for the most part spelled out in stone for the viewer and don't really develop beyond what you see in the first few episodes.
It's a fun series if you're looking for something with lots of action and not a lot of anything else. I didn't go in expecting a deep plot and thoroughly enjoyed it. My only major complaint is that the end of the series feels very rushed, as if the team didn't want to or didn't have the budget to work on it anymore. The show's namesake, Koutetsushin Jeeg, doesn't even appear until the last episode for all of about three minutes, which is a shame because he's really awesome. Besides that it's a great show that's at least worth giving the three-episode test run if you're a mecha fan.
A good place to start here is with what Koutetsushin Jeeg does right. It has a good soundtrack. It has some genuinely funny moments. It has an awesome mech design.
However, it's at its core a reboot of a super robot show that, while hugely popular apparently in Italy, is pretty obscure otherwise in the West. It unfortunately references the original a lot, and has appearances from the cast. It's also a little rushed at the end, being only 13 episodes. Some more episodes to flesh out the backstory, introduce the key plot elements of the ending arc and perhaps just to let some of Jeeg's
forms get more use would make it a lot better.
It's nice to have a super robot show that doesn't take itself seriously at all. The eyecatches are often funny, and very well drawn, and the basic premise of taking a loutish biker and telling him to save the world (while surrounding him with attractive women) is simple and effective. However, the villains are ultimately not particularly interesting, mainly because they don't do very much. Queen Himika is less memorable even than Lord Pasdar from GaoGaiGar, and that's something given she's 100% woman living in a volcano and he's a face attached to a chunk of metal. The enemy designs are interesting for the most part, although not very memorable or iconic compared to stuff like the Mechanical Beasts or the Dinosaur Empire.
JAM Project did a brilliant job with the OP and insert song, one must say, and that's a strong point in the show's favour. The combination sequence (which, if too long or uninteresting, can make watching a super robot show tedious) is largely unobtrusive and used as part of a rather funny scene in one episode - so no complaints there.
Ultimately, Koutetsushin Jeeg is a rushed show. If it had been a full 26 episodes, there's a chance it could have been great on the level of Shin Mazinger, but as it is you feel it's just got going before it's all over. Watch it if you want a funny and exciting show, but be prepared to take its flaws with its strengths.