This time on Warhammer 101 I will discuss the newest Warhammer 40,000 codex: Dark Angels
First the Dark Angels have many units in common with regular Space Marines. If you have any of the following then you can use them in a Dark Angels army:
Space Marine Commander
Land Raider (all variants)
Land Speeders (except the Storm variant)
The Dark Angels have two primary differences from the regular Space Marine list.
The Deathwing- Dark Angels have their own Terminator elite troops. Unlike regular space marines, the Deathwing isn't split up into assault and shooty terminators. The Deathwing can have all combinations from both the assault and shooty tactical versions (with a few more toys). It is also worth noting that the Dark Angels don't use power armor veterans (i.e. Sternguard and Vanguard veterans).
The Ravenwing- This is all the Dark Angel fast stuff. Land Speeders, bikes, attack bikes, and a few jets.
These all have specialized kits so make sure you get the right ones.
This all begs the question:
"What if I play regular space marines, but I want to use the new shiny codex?"
My answer is use the Dark Angel codex. It is likely that the next regular Codex Space Marines will be very similar to the Dark Angels. The Dark Angels Codex is more viable in the current game than the original space marine one. As long as you don't buy the Ravenwing jets and specialized land speeders everything else will have a place in the next marine codex.
This then begs the question:
"Can't I just wait?"
Sure, but the Dark Angels are more tactically flexible. Also you will likely be waiting for a long time. The next Codex: Space Marines is not currently on any release forecast for this year. You really don't have anything to lose by using the Dark Angels book. Only two kits won't be available for the next marine list (Nephilim jet fighter and the Land Speeder Darkshroud). Sure you can't use scout bikers or sternguard and vanguard veterans but that's life. Still recommend the Dark Angel book over the Space Marine book unless you love a special character from the Marine book.