Now this was a surprise. Just read 3 volumes straight and it gets better every single volume.
But... I have to say, this manga is not for everyone, for a bunch of reasons. First off, there is gore. While it isn't the goriest or one of the goriest things around for sure, it definitely contains a significant amount of gore. If you're susceptible and sensitive towards gore, it's probably best to stay away.
Next, this is clearly a manga that isn't too focused on a very complex plot. The main attraction here is violence, clearly. But don't get me wrong. The plot has been moving and there are clear signs of a big conspiracy brewing behind the scenes, something we'll see more of in volumes to come. It's just that I don't think you should be reading this if you're looking for an interesting and complex storyline as that isn't its main focus.
Another thing that might put some people off is the high mortality rate. Like Gantz, this is a manga where a lot of people die. A lot of people you weren't expecting to even. This is one of the most enjoyable points for me - as it becomes very unpredictable and way more thrilling - but I have heard that some people dislike stuff like that. Some people prefer the more... how to call it... "shonen" approach to things, where the main characters get together, form a group and most of that group stays alive till the end. If that's the case with you, this is probably not the best choice.
That being said, if you enjoy these, this is definitely one to check out. I might be jumping the gun in calling it the next Gantz, I know. What I mean with that comparison is that the feeling of those two is somewhat similar. People who are taken to a different place to fight monsters that they can't possibly comprehend. Most of them die, even some that you thought were going to be important characters. The pace throughout the action scenes is fast and stained with ruthless kills (from both sides). The threat our characters are facing often seems completely overwhelming and they have to crawl with all they have just to pull themselves out of it. This description fits both mangas and that's why I made the comparison. Then again, there are a lot of things separating them (for instance, Terra Formars has more dialogue - that both kills a bit of the pace at times and increases the "coolness" of the abilities - and Gantz is more about normal humans that are given weapons whereas TF features superhuman characters).
Lastly, the scientific or historical quotes from actual books was a very nice touch.
I do hope that this doesn't go to sh*t like Gantz did, but that's a whole different matter.