No, Samuel Johnson did not write the first English Dictionary. Let's dispense with that up front. However, he did write an incredibly high quality one, the first high quality English Dictionary actually, and he did it practically singlehandedly. (For the details of the effort, please see "The Making of Johnson's Dictionary," by Reddick, also available here at Amazon.)
Johnson wrote his Dictionary at a time when people read Dictionaries, not just referred to them. Knowing that, Johnson pursued his goal of putting a stake in the ground as to the meaning of words while developing and promoting a point of view; he was very careful about the quotations he used to illustrate his words, and the choices he made have been the subject of numerous books.
Johnson knew, in writing a Dictionary, that any attempt to cement the language was due to failure, and he said as much in his famous Preface. However, he felt obliged to make an effort (heck, he'd already received some advance money, and had to make good!), and over the course of years produced a volume that reigned supreme until the advent of the Oxford English Dictionary.
(You may already be aware of amusing definitions found within, such as oats, pensioner, etc., but it would be a shame to let the amusement distract you from the achievement that this represents.)
McDermott has included both the 1st and 4th editions on this CD-ROM, thus providing the two major editions Johnson produced (other editions are either skeletons, sans quotations, or very similar to these here), and its presence on CD-ROM makes it mcuh handier than pulling two heavy volumes off the shelf (which would cost you thousands of dollars anyway). I only have two regrets, neither of which should stop you from buying this. One, the CD-ROM does not include Johnson's Preface (it is easily available in paperback Johnson anthologies, but the absence seems pointless). Two, unless I haven't figured the interface out, it's a bit clunky: words are not searchable, one must click sections open.
That being said, I am still very glad I have my copy, and I bought a second for my alma mater.