This is a very difficult book to give a star ranking. James Michener was an excellent author, and every book he wrote was readable and engaging. This is true even of this novel, his longest (1,096 pages in the hardcover), but I feel like this book is sort of a misfire in terms of artistic effect. There are a lot of things I could say about Texas, and I made a bunch of notes on it as I read it, but I'll try to keep this short.
The biggest problem with Texas is that Texas (the state itself, which is essentially the protagonist of this novel) is terrible. The novel, Texas, is broadly sympathetic to the story of the state, Texas, but Michener is either unable or unwilling to lie or gloss over the worse aspects of the state enough to make the story sympathetic to anyone who is not already emotionally invested in the state, and the parts where he does try to spin things in a way flattering to Texas are mostly just uncomfortable and ineffective.
To start with the latter point: the Spanish, and then Mexican, governments, are presented as uniformly corrupt and incapable of effectively governing Mexico itself, let alone Texas, to make the Texas Revolution and then the Mexican-American War seem more palatable; and, worse, Native Americans are portrayed as pretty uniformly violent and barbarous, and totally hostile to diplomacy or civilization. There are a few Mexican (and Hispanic Texan) characters, but they are curiously underdeveloped, even though several of them have stories that must be more interesting than the stories of some of the protagonists of the book. There is only one Native character who receives any development at all, and he is portrayed as cruel and exploitative and locked into his futile attempt to preserve his barbarous way of life.
The successive protagonists of the book, spanning 1540 until 1985, are not really much better. They're portrayed sympathetically, but it's a problem when even the most sympathetically-portrayed characters are violent jackasses who murder strangers in cold blood, or KKK members, or murder countless innocent Mexican civilians, or are real estate speculators driven by greed; no matter how sympathetic the characters are shown to be, it's impossible, at least for me, to actually embrace and identify with the experiences of these people, given the profound ugliness of their souls. As in other Michener epics, the characters who are the best people often die abruptly and ignominiously, while the wicked or unscrupulous thrive; however, it's a problem when my reaction to the swift shocking deaths of the "good" characters is relief, because they aren't that much better than the "bad" ones.
Texas itself, as the real main character of the book, is deeply unsympathetic. Every one of the states of the USA has sordid aspects to its history which you cannot honestly ignore, but reading this book one gets the inexorable feeling that Texas is the most sordid of all- that Texas is a vile edifice built on a foundation of, and lastingly shaped by, genocide, racism, slavery, injustice, and violence; and further, that Texans as a people are characterized by being dim, petty, hypocritical, short-sighted, reactionary, anti-intellectual, greedy, and parochial.
The latter is not (uniformly) true in real life, of course, but it's the impression you get from this novel, given the repeated (three or four times over, depending on how you count) cycle the novel depicts: well-meaning white people emigrate to Texas; they work hard and try to be decent people; they are succeeded by their children, who become hateful monsters of human beings. One must conclude that Texas itself exerts a powerful, malign influence on humans who grow up there, turning them into the worst possible versions of themselves.
Jubal and Mattie Quimper immigrate to Stephen Austin's colony from Tennessee and set up an honest business, a ferry and inn; they are succeeded by their son Yancey, who is a coward filled with genocidal hatred for natives, a chickenhawk who aggressively pushes for Texas to secede from the Union and then murders innocent Texan civilians who disagree with this, and a grasping conman who cheats a veteran out of his lucrative business and makes a fortune on it.
Finlay Macnab immigrates to Texas from Scotland, via Ireland and Baltimore. He (bigamously) marries a Mexican woman to secure land in Mexican Texas, then dies in the Revolution. His son Otto becomes a Texas Ranger who is consumed with race-hatred for Mexicans, and who extrajudicially murders dozens of Mexican civilians in the disputed Nueces Strip.
Earnshaw Rusk is a Quaker from Pennsylvania who tries to make peace with the Indians; he is cruelly disillusioned by the natives' cruelty and lies, and marries a much-abused white woman who had been kidnapped, mutilated, and serially raped by the Indians he tried to pacify. They make an honest living ranching. Their son, Floyd, is another paranoid coward of a man, who as a teen murders two men in cold blood in a confused Oedipal rage; later he founds a chapter of the KKK and runs all black people, all Jewish people, and many Catholics out of the town his parents founded. Then he gets rich off oil, and cons his neighbors to secure ever-more oil, and uses his oil riches to sponsor massive cheating on the part of the local high school football team, because having the winning high school football team is a cause that induces religious mania in Texans, I guess.
After all this, there are a few little seeds of hope in the last chapter, showing, in the scions of these family lines, awakening social consciences and appreciations of art and nature, but that's 1,000 pages in; the novel ends with the latest Rusk, with encouragement from the latest Quimper, appointing the latest Macnab (his son-in-law) as director of a museum of sports art he is founding (after "comically" calling up Tom Landry to ensure Macnab is not gay)- but that's after nearly 1,100 pages of the grinding awfulness of these characters and their ancestors, and it's too little, too late.