Scrimgeour isn't portrayed badly, he just isn't in the films nearly enough. He's a very interesting character, a politician who is willing to do some immoral things in his fight against Voldemort. You can immediately see why the wizarding world, in the midst of a terrible war, would prefer him over Cornelius "I Still Refuse to Believe He's Back" Fudge. But he's not exactly a good guy, is he? He has people wrongly imprisoned, to make it look like he's achieving some victories in the war, and he tries to woo Harry into being a poster boy to boost morale (after the Ministry went on a major anti-Harry campaign, to add insult to injury). The later books featured a lot of political gamesmanship, and while that can be boring when it's a major aspect of the film, sprinkling a little bit of that perspective could have added some depth to the story. Scrimgeour was an inscrutable, calculating character played by the always fantastic Bill Nighy, and it's hard to see where it could have hurt the films to feature him a bit more heavily.