In some sense he had less impact than he might have, as he was a confrontational writer, an absolutist in his theorizing, and unsparing in his critique of others, including his fellow justices' opinions. It's what made him so great to read. Had he been a consensus-builder, negotiator, or compromiser his impact might have been greater. But he would have been a lot less fun.
I disagree fundamentally with his dogmatic originalism (and I think Scalia ignored it when it didn't suit him anyway) and I disagreed with - man, it's hard to write in the past tense about him now - the vast majority of what he wrote. But he did change my and many others' minds about interpretation of the Second Amendment. And he was a staunch champion of reining in government excess. He opposed the idea of special prosecutors, warning of exactly the sort of out-of-control prosecutorial license that we have seen in cases like Aaron Swartz. He likewise often championed the rights of defendants to have errors and misconduct at trial rectified.
Our legal system is poorer for his passing, and his untimely death will now become the epicenter of a firestorm of political idiocy around appointment of his successor. It's ironic that the man who most visibly championed following (what he saw as) the Constitution's original intent will become fodder for a rebellious Senate that seems bent on ignoring its Constitutional role in replacing him.
Article II, Section 2, Clause 2 reads in part:
The President [...] shall nominate, and by and with the Advice and Consent of the Senate, shall appoint Ambassadors, other public Ministers and Consuls, Judges of the supreme Court, and all other Officers of the United States
That is, the role of the Senate is clearly to advise and to consent and not to refuse to consider and not to railroad and not to threaten. That we seem poised to see otherwise is a smear on the legacy Scalia will leave us.