Well... Manga itself is great, though visual novel brings a bit more enjoyment. So if you have spare time, I'd really suggest you to read VN due to fact that it has more in it, also it is worth to read prestories (Unlimited and Extra) cause there are sometimes things that would be immpossible to understand unless you read these 2 previous firstly (on the first hand tho you will be totally amazed HOW from Extra -> a funny, romance story, we have got something like Alternative that is rather sad, sad, and SAD story (in the end) with awesome action, great characters and a little gore moment (well that one hopefully won't be in manga)).

If you love series like Gundam, Evangelion -> VN and prequels is MUST READ. If not... It is still WORTH reading (I can't recall any good manga recently that had same lvl of action as this one, and so well build characters).


Still sadly VN is heads over manga, but if you can't simply read VN, go ahead with manga and "enjoy" world where humanity struggle, and are trying to avoid path of extinction.