all spartans in campaign and multiplayer are spartan llls exluding Jorge, which Azaxx stated above
Spartans l were just basically elite soldiers hoped up on strong drugs (not cocaine and what not obviously)
Spartan lls were a much more radical soldier, they were kidnapped at the age of 6 and put through EXTREME training, until the age of 14(not sure on that) when they were given augumentations
Spartan llls were basically cheaper spartan lls, given weaker armor, and almost ALWAYS sent on suicide missions en mass.
Now that's out of the way, I think the Cheif looks more badass than ever before, since you can now see the rough outlines of his body, giving him a more intimadation look imo, and if anything, I think Halo 3 looks more cartoony than Reach, I think Reach is a bit more realistic than 3, well... for a sci/fi shooter