Overall, i would say yes. He seems nice and caring from even before timeskip as he had his crew. But we know that Law's crew is stuck somewhere on Zou. So like many others have stated, i think he wont betray Luffy but break off the alliance eventually after they take out Kaidou and be like :
~~~~~~~~~~~
Law: " since, we are both going after one piece , we can no longer be allies, mugiwara-ya!"
Luffy: " shisshishi. Okay then. Jaa na!! "
So essentially, Law is a good guy. Heck he saved Luffy's life twice. Once in the war and now from the poison gas. Basically what he wants is to get his crew back and destroy the guy mainly responsible. He would do this because remember what Eustass Kid sayed:
" That Law, whats he planning!? He is usually known for his brutality".
But then again, is still an Pirate and pirates are deemed as evil. So there really cant be adefinition of "good or bad" in the OP world as some pirates as well as marines are swayed in opposite directions.