Upon rewatching this thing a couple of days ago I was struck by how the main villains are surprisingly not particularly villainous. Oh, Eric is definitely a threatening and intimidating guy, especially when backed by Colonel Nsogbu and his men, and he certainly isn't above killing people to get what he wants, but what I mean is that there's some hints here and there that Eric used to be a good man but was just driven to the dark side if you will by his obsession.
Take for instance the scene where Nsogbu's men kill the male brontosaurus. They're shooting and Eric is yelling, "Stop them, for God's sake!" and when the damage is done and the dinosaur is dead, an incensed Eric asks the Colonel, "Do you have any idea what you've done?" Sure, one can argue that Eric is only interested in the brotosaurs' welfare insofar as his research is concerned, but when he later kills Nsogbu for constantly giving the female too much tranquilizer, there's an underlying feeling that there's more to it than simply that. Also at the end when he thinks Baby is dead, there's genuine sorrow in his eyes.
And then there's Nigel. Whereas Eric prefers to hide his emotions Nigel is openly concerned about the dinosaurs and whines constantly about whether they're doing the right thing. His overzealous behavior when he jumps into the water to get the sedated female's head out of the water so she won't drown, and when he's later trying to comfort the caged Baby ("She's just so scared!"), clearly demonstrates he isn't an evil man. He's just kind of a wimp who does whatever Eric tells him.
Some good writing in this film. A lesser movie would've made Eric and Nigel out-and-out villains but instead the script, and their actors, allow them to come across like real people.