Patience with Gantz

I decided to watch Gantz and finished it the other day. I was interested because it has a weird plot and I`m searching for a good read but then since it has an anime version -- I guess I`ll just watch it and decide if I`m gonna read it right after.
Gantz is totally confusing. After watching the anime, I decided to start reading the manga since I can`t get to the bottom of things and FYI the manga is licensed and is distributed in 5 languages so it got me thinking that it really is a good one. It is still ongoing BTW and it`s now at 306 chapters.
First of all, the anime starts with the main character and an old friend dying at the subway while trying to save this homeless drunk who fell in the subway tracks. After getting hit by the train, they found themselves inside a room with a bunch of other people and a huge black sphere. The story starts rolling when they were to kill this certain alien as a mission but people started dying one after another. What`s going on behind all of this? Well, after watching the anime, I never got any answer so I have to resort to the manga.
Everything in this anime is very good although I get to experience clenching my fists and my heart racing in long durations of time. WHY? Lets just say, the action scenes are unique and your patience tested to its limits. There`s a lot of blood and gore in this anime. There are also ecchi scenes for anyone who likes watching those kind of scenes.
I don`t recommend watching this for the faint-hearted and the short-tempered.
Enjoy!