I was introduced to Alan Moore through "Watchmen", "From Hell" and "V for Vendetta", all of them essential reads. "Saga of the Swamp Thing" is an early work and while it already shows Moore's intelligence and potential, it isn't as satisfying as the titles I mentioned. I have the feeling that Moore was trying too hard to please the "comic horror" public by playing along with some of the silly conventions of the genre - notably the insistence with which demons and all sorts of monsters spring out of the ground to terrify the human populace for no reason. I mean, the "Monkey King" was well constructed as a representation of fear and paranoia, but the minute that other yellow demon comes along to do battle it all gets a little too much for me.
I enjoyed the first story arc, where Moore reinvents the figure of the Swamp Thing and, through the conflict with the Floronic Man character, reflects on environmentalist issues. The plot of the second storyline was more shallow, too "mystical hack n slash", and dind't deliver. The Swamp Thing's role in it is completely arbitrary.
The art is very good (the swamp scenes are mesmerizing in detail and colouring), although perhaps a little dated and not for everyone's taste.
With that said, although I am curious to find out what happens next, I will take my time and read some other stuff before going on as it did not exactly grip me.