A major concern many conservatives have with Kagan is that she's got a history of some pro-union/pro-organized labor rulings. With Garland, he appeared to be quite moderate, but there were a lot of concerns about his take on the 2nd Amendment. I have not personally looked up many details about his rulings, other than he seemed to be largely pro-police and pro-prosecution.
For Conservatives, I think the judges are often important because there's a general fear of government creep into personal freedoms, and the Supreme Court is the last place to stop it. 2A infringements, race-related entitlements that are discriminatory in their attempts to "re-distribute" cultural representation across industries, squashing of the guarantee of religious freedom, etc.
And, to Chris's point, there is no doubt that there plenty who want to see Roe/Wade overturned.