Obama isn't even trying to be in the political center after the last election. He is now going to go all out in a liberal partisan manner, and his inauguration speech demonstrated this. He is now completely about leftist politics, and will be for the rest of his Presidency. His days of apparent compromise are gone.
His beliefs are not partisan. They are actually quite moderate and only slightly liberal. The people who think otherwise are a little disconnected from history, as much of what he argues for are things Republicans used to support not that long ago. It was a fair address to his fellow citizens and was completely appropriate.
Obama's speech did not address partisan issues, but instead real issues that face America and that, of course, people have partisan views about. The fact that people have differing views does not mean that they are not real issues that need to be addressed. For instance, issues of immigration, gun control, or gay rights are in some sense constitutional issues that cross party lines. Political parties tend to have opposing views on these issues, but it is not a partisan stance for Obama to announce that he intends to address them.
Although some people believe Obama's speech was too partisan, in my opinion it was not. Obama addressed issues he thought were important to the American public. Not everything should be seen as a war between Republicans and Democrats -- maybe we should look at the issues Obama addressed as issues relevant to everyone in America, no matter their political side.