Zegapain is really good. Along with Fafner those two are my favorite mecha shows. Though Zegapain is not exactly centered around the mechas ... more like the setting involves mechas, rather than it being the central point. A very satisfying watch. SciFi/drama/romance/action. Thats pretty much all i can say, as the series is easily spoiled
Not going to say anything about Guren, as i stopped watching at ep5
Planning to watch it sometime though. Though the portrayal is more on the goofy side