The difference between all of the Space Marine codexs?
In short nothing besides special rules, sculpts of minis, and some unique units.
This is mostly because everyone, except the Space Wolves, adhere to the Codex Astartes that dictates a lot of the unit/army designs before the player gets involved.
It's really hard to say that they are the exact same at the same time
Blood Angels are the kings of the sky, with their affinity to Jump Infantry they tend to prefer close combat slightly more than the standard SM army.
Dark Angels tend to favor a heavier mix of Bikes and/or Terminators compared to generic Space Marines.
Black Templars are able to field large waves of marines that, for loyalists, is unique to them.
Space Wolves are special themselves, as they don't really fit into a standard "Space Marine" mold that almost all of the other chapters can. They are umm... Space Wolves, I cannot describe them as anything else, they are legitimately vikings in space, they are brutal when they are in close combat and they are perhaps the best bolter ranged armies in the game.
They excel at Drop Pod assault, since they have the Counter Attack USR they (the player) don't really fear being in close combat after arrival, compared to most generic Space Marine units.
I hope that helps at least a little bit.
Originally Posted by neilbatte
if you squint the Sigmar stuff doesn't all look like the love children from a Necron and Blood Angel orgy.