Justice Kennedy's tenure has earned him a reputation as the "swing vote" in many of the landmark cases he has seen. He is considered a reliable vote for all things Gay Rights having voted with the majority in Romer v.Evans, Lawrence v. Texas, United States v. Windsor and Obergefell v.Hodges. It is hard to imagine his replacement will continue that support.
Kennedy's other major decisions included:
Citizens United v. FEC
Kennedy found that you cannot restrict free speech from corporations and unions. This overturned a law that limited/banned them
Texas v. Johnson
siding with the majority that flag burning was protected as free speech.
Boumediene v Bush
siding with the four liberal judges that detainees at Gitmo and those designated as enemy combatants have a right to habeas corpus
District of Columbia v. Heller
Kennedy sided with the conservatives and ruled DC's ban on handguns was unconstitutional
Florence v. County of Birlington
Kennedy ruled that people detained and admitted to the general population in prison were subject to strip searches.
If you want to know why all the snowflakes are melting down it is this: Kennedy was a moderate. He could not ever be claimed by either side as a dependable vote for Liberalism nor Conservatism.Liberals will want an identical candidate to replace him and quite frankly, Justice Kennedy proved over and over he was one of a kind.