As has been mentioned, a defining aspect of the Reacher character in the books is his giant size.
Ellie's appearance has absolutely no bearing on her character. I don't think it's even ever addressed once in the games. That's the important difference.
I dont understand why they would address her looks for her character in the game anyways, that makes no sense.
fact is she just isnt a good Ellie, she doesn't look remotely like ellie, doesn't act like her, doesn't have her mannerisms, doesn't even talk like her, she's not even the same character.
either was Bill in episode 3. (it may have been a good episode) but they changed everything about his character too, a guy that trusts no one and so stuck in his ways that he drives Frank to abandon him out of hatred but getting bitten in the process and then committing suicide, they dont go out together in a crappy love story, Bill continues on by him self.
one change I did like was them making Sam deaf, I dunno it just fit well. but all of that was rushed too.