This was a good result for Nadal in his first tourney back. You cannot just expect a guy to come off a 7 month break and win tourneys no problem. He got to the final and played a tough match. He will have to be better to make a good defense of his clay points but as long as the knee isn't a huge bother his form will improve.
"Everybody has a game plan, until they get punched in the face" -Mike Tyson