As it relates to executive action on the part of Reagan as it relates to illegal immigrants in this country, again it's not comparable to Barack Obama in this instance. I'll refer, as I have often, to Justice Jacksons decision in Youngstown Sheet & Tube Co. v. Sawyer that serves as the basis for the legality of executive action in this country...
The presidents power as it relates to executive actions is at it's most when said action is pursuant with the express or implied will of the Congress. This applies in situations relating to Reagan's executive action in 1987. The congress had just passed a law the year before whose clear intent and purpose was to largely grant amnesty to the majority of illegal immigrants in the country in order to humanely allow them to remain within our country. Unfortunately, as happens in comprehensive large laws, there were unforseen issues that arose...such as situations where one member of a family fell under the parameters of amnesty while others didn't. The Presidents executive action in that particular case was in line with the expressed and implied will of congress as it related to a law passed under that very congress, and signed by that very president, in regards to altering the enforcement of that law.
The presidents power as it relates to executive actions is at it's lowest when said action is imcompatible with the express or implied will of the Congress. In this case, Congress has passed no law recently related to immigration and is...at best...split on permanent or temporarily allowing illegal aliens to stay within the country. The incoming congress less than two months away is clearly against such things. NOTHING past by this congress suggests in any way, shape, or form that it's implied or expressed will is to allow ANY illegal alien to remain here temporarily. Indeed, laws specifically aimed at doing such...like the DREAM Act...have failed to pass this congress.
Reagan was acting based off of a piece of legislation, passed by congress and signed by him, that was less than a year old in which said [executive] action was in line with the implied or expressed will of congress as it related to the purpose of said legislation.
Obama would be acting based off no such legislation signed by him or passed by this congress and would be acting in a way that is incompatible with the expressed and implied will of the congress.