I watched Chaos;Head first, thinking it was a prequel and was necessary if I wanted to watch Steins;Gate. Well, it wasn't. I was actually very surprised at how much I liked this in contrast. I realize the story isn't perfect, and there were a few inconsistencies, but these were pretty insignificant and easy to ignore.
Or at least, I thought they were inconsistencies. It was hard to tell which day the main character would return to. It was even hard to tell how many days have passed in regards to the d-mails sent. And, if the main character had been travelling back in time within the time span of 2-3 weeks, how were they able to surpass the 48 hour limit to which they could travel back? I'm guessing everyone didn't send their d-mails in a 48 hour time span.
He also managed to go back in time with two different methods. Well, three if you count the time machine from 2036. The first method was through text messages. I get that. The second message was sending memories from the future to the past through some kind of machine Christina made two days prior to Mayuri's inevitable death. So, if he traveled beyond those two days prior (which I think he did because he went back in time to reverse the d-mails made previously) then how could he transmit his future memories to his past self without the machine she created? It seemed the writers would mix up the changing of fate with him leaping back in time. If that makes any sense.
ANYWAY, if you decided to ignore the confusing chunk of text I was rambling about to myself in order to get a better hold on the story, here's my overall review:
Great animation and I thoroughly enjoyed the characters as well. The story development could use some work, going from gel-bananas to humans transmitting memories back in time, to time machines. Even SERN kind of disappears from the overall story towards the end. Regardless, I still enjoyed watching this anime. I always base my anime ratings on how engaged or interested I was in what was going to happen next. I watched this entire series in two nights. I'd say I was pretty engaged. Interesting story, fun characters, and great animation: 9/10