I'm not sure when these comics first came out. I'm guessing in the late 1960s. Stan (the man) Lee wrote some of them. Herb Trimpe and Sal Buscema drew most of them, and it would seem that Sal Buscema was new to Marvel at this time.
Another reason that I'm guessing 1960s is that Doctor Strange appears in the first half of this collection, and his "astral form" in this issue is different from that seen in later Doctor Strange comics. The Rhino and the Absorbing Man are new characters here, with the Absorbing Man having just appeared in the pages of Thor.
I really enjoyed this one. Compared to the 1980s X-men I just finished, these comics were a breath of fresh air. The plots are simple, the art is bold, and the Hulk is busy smashing his way through adversary after adversary. The writing in these comics is very consistent. They are writing and drawing to a formula, but the formula works.
Reading this, it's easy to see how Marvel overshadowed DC during the latter part of comics' Silver Age. DC comics were also driven by some great ideas during this same time, but Marvel always had that moral ambiguity that DC lacked. The DC universe was, for most of its history, a universe of black and white, good and evil. In the Hulk and other Marvel comics, however, we find a universe where black is sometimes white, and good is often evil. The early Hulk comics epitomize this trend, and it is easy to see why comic book readers of the time responded to it. Marvel was, in its way, more authentic.
I'm hoping I come across more of these Essential Hulks in the future. I would be eager to read more!