Space Marines are here once again! With the new codex, there are lots of folks talking it up. Many people are suddenly reinvigorated with 40K, and a number of people (myself included) are spying a new army in the future. That being said, I MUST resist the shiny! I struggled with the "choosing a chapter" some time ago, and I must stick to my guns! In the end, I LOVE the Grey Knights, and I have since my beginnings with 40k. When their codex was released, I fell in love again, particularly with the beautiful plastic kits. Besides, I have a newer more feminine project down the pipes :P.
I do appreciate one major addition/modification with this codex: Chapter Tactics. In the 4th edition codex, there were a number of rules and added benefits that players could choose to add to their armies. 5th edition codex, however, locked these variable rules into special characters that didn't always fit the theme of the DIY chapter (which was my intended goal). An example from my own thinking: I was thinking about a chapter called the Mountain Kings. Their fluff revolved around building large fotresses built into the sides of mountains, caring for the Imperial citizens below. In order to follow this kind of fluff, I had to take Lysander. Well, Lysander has the Fist of Dorn as a weapon, clearly an homage to the Imperial Fists. With this book, I can now take the Chapter Tactic: Imperial Fists, giving that part of the Fluff ( and helping with story as an Imperial Fist successor chapter), but I can use a Grand Master instead. Options like that really give me a greater range of freedom with the codex in terms of a DIY chapter.
I think the codex will also provide Marines players with some help adjusting to the Xenos dominated metagame. Space Marines have really powerful rules aiding them: allying to themselves, new wargear, Centurions and even the AA tanks can lend a hand. I'm looking forward to whatever may come with the Space Marines.