I thought you stopped watching early on?
Anyway, it does make sense that the show focuses so much on the Tea Party and how it has come to dominate the Republicans because both Will and Charlie see them as a great danger. It's also an important part of the overall arc of the season because going after the Tea Party and the crazy Republicans is what gets Newsnight on Fiona's and Reese's bad side. It's also very plausible that Will would be so invested in pursuing this because he's himself a Republican (a moderate/liberal one) and sees his party taken over and shift to the right.
Also, let's keep in mind that, all things considered, we only see very little of the actual Newsnight
content, considering it's about 45 minutes long each weeknight. The show can only show a small selection of what they did.
Also, there was minor criticism of Obama's reaction to the Deepwater Horizon spill, though it wasn't on the news show (Gary and Kendra were arguing about it). I suppose, the show where they talked about the development of gun laws under the Obama administration can also be seen as criticism even though on Newsnight
it was only used to show how Republicans/the NRA/conservatives were lying about it. Will saw it that way as well, but his date (Sloan's crazy friend with the gun and the marijuana in her handbag) thought that they had come out against guns.
Lastly, it's a romantic comedy with some drama and a politcal slant. They are in no way obligated to be balanced or even accurate.