Depends.
If you want to play regular Space Marines (I.e core of tactical squads supported by other units), then Dark Angels are not a brilliant choice. Their book has many pieces of equipment that are weaker than in the normal
SM book, so you might as well just use that and keep the
DA Fluff and colour scheme.
BUT
If you want to play an all Termiantor or all Bike list, Then
DA are fantastic. Okay so you have to take a special charector (Belial for Deathwing terminators, Samael for Ravenwing bikers), but look at the pro's. All your units are either fearless or a vehicle, you get a fast moving and tough force, decent weaponry, and interesting Fluff. Unfortunaetly, you won't be able to paint the Green you were talking about if you use standard Death or Raven (Or DeathRaven) wing lists, but hey, that's what successor chapters are for.