For those who are complaining the President has exceeded his Constitutional authority by circumventing the legislature, irony alert: The Executive Order is the quintessential act of the President fulfilling his Constitutional responsibility under Article II to exercise the "executive power of the United States." An Executive Order is simply an instruction from the head of the Executive Branch to the relevant personel under the authority of the President pursuant to Article II on how to execute the laws passed by Congress or how to fulfill existing regulations authorized by Congress or how to implement some other Administrative function. Usually these are quite dull things, such as an Excutive Order directing the General Services Administration to establish an "Innovation Fellows Program." Sometimes these have broad policy implications, but are still just instructions on how the President wants the agencies under his authority to act, such as this Executive Order on Using Behavioral Science To Better Serve The American People.
Keeping this in mind, lets review what the President actually did as his Executive Action on gun control.
To conclude, I get that "Executive Order" has now become a trigger word that acts to most folks as a huge distraction -- especially non-lawyers who don't know what an Executive Order actually is and how it works. But Executive Orders are nothing new and are in no way "bypass" Congress -- at least not in a Cnstitutional sense. Executive Orders are directions from the President, the head of the Executive Branch under Article II of the Constitution, instructing the relevant agency heads and other relevant personnel subject to the President's authority under Article II to do something. It is roughly the equivalent of a memo from a company CEO/President to folks in the company on company policy.
The bottom line here is that the President Obama is limited in what he can do under existing law, so he has used his interpretation of existing law to do what he can. Far from a violation of the Constitution, it is the specific job that the Constitution requires him to do as his #1 priority as head of the Executive Branch. Existing constraints on executive action, as always, remain enforceable in the Judiciary, and Congress may, in turn, may perform its core Constitutional function -- legislation adn appropriation of funds -- to reverse the President's action. People should feel free to debate what they think of the policy, but it would be nice if they actually understood how our system of government works.