I recommend doing several loads of laundry, and then folding it while watching this movie. I actually don't mean that in a bad way. It is a mildly entertaining, if overly long, 3 hours or so.
As you can tell from the very mixed reviews, whether one likes this movie might depend on your mood and your willingness to suspend disbelief and take Creature on its own terms. As other reviewers have noted, this is Peter Benchley ripping off himself in subpar manner. On the other hand, the creature is kind of cool, there are some really nifty sets, including abandoned tunnels, abandoned laboratories, abandoned military facilities, foggy swamps, and mysterious, shark tooth-shaped Islands silhouetted against the full moon, and for the most part the acting is more than adequate. Taking it for what it is, I would give it 5 1/2 or 6 Stars.
Note, regarding the DVD: As of this writing, 2019, Amazon was selling a 2-disc DVD set released by Olive Films, for around $12. The picture is excellent, surprisingly detailed and crisp, and presented in the original 1:78 widescreen. The sound is also very clear. Unfortunately, and unforgivably, there is no closed captioning. Not surprisingly, there are no special features. I do like the fact that it is presented with parts 1 and 2 each on its own DVD (labeled Night 1 and Night 2, which is kind of neat), so compression ratios are fine. I also appreciated the fact that they presented each part in its entirety, including opening and closing credits, unlike, for instance, the commonly found DVD release of Salem's Lot, which eliminated closing credits of part 1 and opening credits of part 2, combining it into one feature.