"I had high expectations and I have to say, when I first watched the movie, I felt really let down, for a number of reasons," Webb told ABC News Thursday. "It's hard to capture someone's life in two hours, and I get that, but I felt the film could have been, should have been, a military epic on the scale of a 'Saving Private Ryan.'"
But Webb said when he thought about it further and when the movie started a national conversation about the hardships of American troops in combat and at home, and their portrayal in Hollywood, he came to appreciate the film more.
Still parts of the movie nagged at him. While attending a firearms expo in Las Vegas, Webb told ABC News what he thought "American Sniper" got right, and what it got wrong.
On Target: Chris Kyle, Impossible Decisions, Troubles at Home
The aspect of the Clint Eastwood film that struck Webb the hardest, he said, was Bradley Cooper's portrayal of Chris Kyle. Webb said he wasn't terribly close with Kyle while they were SEALs together, but after they each left the service, they became closer friends.
That's why it was surprising when Webb said that at certain points in the movie, he forgot that Cooper wasn't Kyle.
"There were moments in that film where I thought I was watching Chris on screen. So Bradley Cooper's performance, I thought he nailed it," Webb said.
Webb said that another part of the movie was right on: the dramatic, on-site calls that snipers sometimes have to make while looking down their scope. In one scene, featured in trailers for "American Sniper," an anguished Kyle watches as a child picks up weapon, making the young boy a potential target. Webb didn't discuss the moral implications of such decisions, but said that they are in the hands of the snipers themselves because they can react with the most "precision."
"The situations that Chris is put into as a sniper, having to make those judgment calls... this isn't President Obama ordering a drone strike that's potentially going to come with a lot of civilian casualties as a result of that, just as a collateral consequence, you have Chris making these decisions and really being a precision tool," Webb said.
He said the movie also accurately showed the struggles of some troops coming home.
"Chris coming home, and dealing with that, going back and forth from America to Iraq, seeing that effect play out in real life, has completely changed my opinion of the movie" for the better, Webb said.
Off the Mark: Technical, But Deadly Details, Sniper Training
When you've spent a chunk of your professional career as a military sniper, Webb says it's hard not to notice the little things that the average movie-goer wouldn't think about.
"That's the part where I'm critical," Webb said. "The basic stuff: a cover over your scope. Because we're really concerned, especially in an urban environment, about eliminating that [reflection]. You don't want to have a piece of glass that's a signal mirror on the battlefield... Here's one of the most deadly snipers in military history and he doesn't have a cover over his scope?"
Webb also took issue with the chunk of the movie that covered Kyle's sniper training. He realizes he's not objective when it comes to this, since he said he helped reinvent the program that the real-life Kyle actually went through, but he still thought the segment trivialized an incredibly physically and intellectually demanding course.
"[The movie version] was just very amateurish," he said. "I'm not saying let's give the world a look at exactly how the SEAL sniper program is, but it's one of the best programs in the world and I thought that [filmmakers should] at least give it that respect that the program produced this guy... You're going to show his training like it's a couple of rednecks plinking at cans in the back of a trailer? That's what it felt like to me."
"But I'm biased," he added.
As for the celebrity-spawned controversy that followed the movie, Webb, who now runs the special operations website SOFREP.com, said he's not too worried, and believes that a majority of the people who go to see the movie are brought together by it.
"They're walking away with a very humbled, positive experience, in that they're learning about this guy that's not a guy that's out there wanting to go overseas and do bad things to people. This is a guy who served his country, who did what was asked of him and this amazing sacrifice and how it affected his family at home."