Dave gave a pretty good answer to your question. I would add that it seems to me that Calvinism is not legalistic at all. If we are all totally lost and incapable of earning our salvation, than obeying laws would have no point.
Basically, Calvinism is known by an acronym: T.U.L.I.P.
1. Total Depravity (also known as Total Inability and Original Sin)
2. Unconditional Election
3. Limited Atonement (also known as Particular Atonement)
4. Irresistible Grace
5. Perseverance of the Saints (also known as Once Saved Always Saved)