I am of the opinion that the previous Space Marine book was one of the best codices written in the previous edition in terms of internal balance and variety of effective builds. It certainly lost some steam as the years went by and some units were clearly over costed, but it remained a characterful book that allowed you to play a ton of different builds that were both true to the fluff (largely) and effective. That is a win. The Dark Eldar book also pulled this off, and I really enjoyed that one as well.
With this newest version of GW's flagship product, we see that they took the previous template that worked so well, and simply fine tuned it. Well done. If it aint broke, don't fix it.
So, what we have is a book that allows you the player to build a HUGE variety of builds that are effective. I really feel that this is one of the best balanced books to have come out in ages. The nice thing about this book is that they took the character of chapter tactics, honed it, and then built in a system that limits overlapping rules and potentially game-breaking combos by prohibiting special characters to certain chapter tactics. That is a nice, elegant solution to some of the craziness that we see with Tau/Eldar or Tau/Tau, for example. The game is most fun when it's balanced, and this to me, is a good sign.
As for the Chapter Tactics themselves, I think they're all very good. Some jump out as more powerful right away, but in our play testing, limited so far but we're getting a lot of games in (check out our YouTube channel as we start to get the SM bat reps edited and up on the site) we've seen that they're all good when used correctly.
The great thing about the book is that you can play it in SO many different ways. You really can go crazy with it. By allowing allies within the codex, you can cherry pick some great units to fulfill specific roles and really take the level of customization in your force to the next level. You have a wide variety of effective and points efficient shooting and assault units to bring a true TAC list to the table, and combined with the special rules of your chosen chapter(s) and/or special characters, the skilled gamer can really build a great army.
One of the other aspects of the book I love, is that fact that you can build super flexible and powerful characters, completely custom! The wargear in the book allows you to make your own unique hero to forge some serious narratives. That is super fun as customization in 40K is one of its most appealing aspects to me and why I prefer it to games like Warmachine which lack that (although Warmachine is a great game, too).
As we are just dipping our toes into this big book, and all I can offer up so far is limited knowledge, I will say that my off the cuff impression is ultra positive. I think GW hit it out of the park with this book and while the nay sayers may be saying Marines can't hang with Tau or Eldar, I totally disagree. This is a book that provides a plethora of tools for the tool box and will please both the casual and competitive gamer. Well done, GW.
More data to come soon!