Should I accept this trade offer?

Absolutely. Ryan Torain is going to become the absolute feature back in Washington, if he's not already. He is so much better then Brown. The only thing I can see a problem with is that you lose Brandon Marshall. So you pick up a better RB, but you lose in WR. Though to be fair you can pick up really any receiver and you'll be ok. You could even look to pick up either of the Mike Williams or possibly even Lee Evans or Jordan Shipley. But you have to focus on the fact that your getting Torain.