About damn time I say. Republicans have been complaining about this for some time. Ultimately, put up or shut up. If you honestly believe that the Obama Administration has been taking significant steps that are exceed the powers of the Executive then it's the duty of those in congress to attempt to provide that check and balance. If members of Congress...and note that some Democrats have even voiced concern on this issue...believe that the Executive Branch is oversteping its bounds then it's incumbant on them to take action to combat that. Whether that's impeachment to remove the POTUS or bringing suit in an effort to invalidated the actions taken, SOME sort of check needs to be done if that's what they honestly believe is occuring.
What will come of such a suit is an entirely different question, but based on what's been said for years this is the proper act on the part of congress. And I prefer them bringing suit over attempting impeachment at this time.