I've never played space marines and honestly never thought that they were anything special, dispite them being so popular. They are/were always a jack of all trades army, which is appealing to many, but when you break it down the xeno/daemon races are so fun because they are specialists that excel at one or two skills; as oppossed to the marines that can do everything but half assed.
I think the current Grey Knights codex is the BEST marine codex, like ever. Want terminator troops? No problem. Want Jump troops? You got it. Want to take hordes of inquisitoral forces? Sure thing dude. The Grey Knight codex gave the marine player a way to specialize while retaining an impressive "Halo-like" variety of weapon choices, the best the imperium has to offer.
So in the new dex, hopefully they follow this theme of being able to run 3 or 4 specialist builds while still retaining their iconic theme.
The only thing you can count on the current dex to give you, is the fluffy feel that you are literally in the 41st millenium, and outnumbered and outgunned by the "scary" xeno races that want to destroy the "good guys".
I will say that GWs release rampup is very awesome so we can hopefully see the new book very soon. Also all the 6th ed codexes are pretty awesome too.
But remember you are a badass because your army is "Old School". So until the new codex hits shelves, make sure after you deploy your Ultramarine smurfs, but BEFORE you roll the dice.. make sure you physically drop to the same height as the models and scream... "YOU'RE MY BOY BLUE!!!"
