I liked Jamey Sheridan, Rob Lowe, Gary Sinise, and Miguel Ferrer's portrayals. Ferrer particularly added dimensions to Lloyd that didn't exist in the books and it was nice to see. Corin Nemec also did well in protraying the jealousy of Harold, but he didn't do so well in portraying any other aspect of the character, though admittedly a lot of the reasons for Harold's fall (particularly the diary) were omitted. I never liked Nadine to begin with, so it's hard to judge Laura San Giacomo's work. It also cemented my eternal dislike of Shawnee Smith and my belief that she shits up everything she's in.
As far as the portrayal of the story... I think seeing it on the screen highlights the some of the central weaknesses of The Stand. The entire thing comes to a drag in Boulder. Mother Abigail is still an extension of Steven King's favorite trope. The religiosity is still heavy handed, but it's admittedly magnified in the miniseries when you're actually seeing the goddamn hand of God touch off the nuke. The biggest losses to the story in the filmed version are explorations of Harold and the fact that they didn't really address how fucked up it was to program Tom, which robbed Fran of some sympathy.
I think it's an underscore that not every book needs to be made into a movie/series. Some books, because they're otherwise contained or easy to show, like Shogun, benefit from adaptation. Others are best left to the written word and the imagination of the reader.