Ah, the Free Spirit! That ethereal creature who blows into the life of an Ordinary Schlub and rescues him from his humdrum life of depression and repression! Does such a character exist anywhere but in the movies? Probably not, but the movies certainly are chock full of them, and here comes Geena Davis, taking her shot at the type and giving The Accidental Tourist the only shreds of life it has.
The fact that Davis seems anything like a real person is an accomplishment, because the script buries Muriel Pritchet under a mountain of quirky -- she dresses funny; she sings goofy cowboy Christmas songs; she has a sickly, hypochondriac son; she's a professional dog trainer -- she's nothing but quirks.
Even Davis's physical presence is quirky, and the movie takes great advantage of that. For the first half of the movie, Davis is never allowed to enter a scene face first; she's always shot in a way that emphasizes her height and angularity -- long legs, pointy shoes, extended fingers with absurdly long press-on nails -- and only then do we see her face. (Even her car is large, an old clunker with giant tail fins.)
Davis brings great warmth and likability to Muriel, and it's easy to see how she can break through even the industrial-strength blandness of William Hurt's Macon. What Davis doesn't make clear is Muriel's attraction to Macon; what does she see in this gloomy lump of a man?
And she's clearly interested in him from the moment they meet, when Macon brings his dog to be boarded at her kennel; she's immediately asking about his personal life and marital status. "I'm a divorcee myself," she chirps; "I don't live with anyone, either," she announces on her first visit to his home. Perhaps she's simply an uncontrollable flirt.
Also inexplicable is the sudden personality transformation that Muriel undergoes heading into the movie's final act. She and Macon argue when he suggests that her son should go to a private school; her protection of Alexander is entirely understandable ("don't you make promises to my son that you won't be around to keep"), but the argument also triggers a possessiveness and demands for a commitment that we'd seen no signs of before.
Even stranger, she follows Macon to Paris, becoming Crazy Stalker Lady; it's as if the movie's suddenly become Fatal Attraction: The Sitcom. This Muriel is just as warm and chirpy as the earlier Muriel, but the obsessive refusal to go away comes out of left field, and Davis doesn't make Muriel's transformation at all understandable.
The blame, I think, lies more with the writers than with Davis (Frank Galati and Lawrence Kasdan adapted Anne Tyler's novel), but since we can't understand Muriel's attraction to Macon in the first place, much less what turns that attraction into obsession, Muriel never makes the leap from lovable pile of charming quirks to real person.