By and large, yes. The tone of comics in general has shifted some over the years, so there's definitely eras, mostly in the way the stories were told. But by and large, the overall character has remained pretty much the same. Truth, Justice, the American way, the big blue boy scout… have been corner-stones of his for a long, long time.
The tone of the books have changed from comedy to sci fi to farce to soap opera to whatever else, and the various tv series between the 50's show, Superfriends, Superboy, Lois and Clark, Smallville, TAS, and more have had different feels and intents behind them, matching whatever times they're in, but the core character remains the same and has largely remained the same since the Fleisher Cartoons and the 50's television show, for the reason that's what people like about the character, its what makes him iconic.
Batman has morphed far more heavily and changed far more with the era he's in.
He has not been that in a long, long, LONG time, and only briefly. You're pointing out the minor extremely rare extreme to make a point. He's been that way in a handful of comics out of thousands, and hundreds of tv episodes. That's not the version of the character that evolved through hundreds of artists and writers that people attached too.
Batman started out willing to murder too, but now his unwillingness to do so is such a part of the character it doesn't matter that he started without it, its part of the icon now.
If that was the case, then Superman Returns would be widely beloved, and Superman 3 and 4 wouldn't be heavily derided and joked about.
It wasn't JUST the incarnation of Superman of the era that made the old movies work, there was a lot more to the actual film itself, including tone, approach and subject matter.
Isn't the reverse also true, that your apparent dislike for the classic characters, and hopes for the new movie (that you haven't even seen) is biasing you towards the new one?
You can tweak the origin or alter the reaction of the characters around him, you can balance the powers to what the story demands and to the point that makes it interesting. You can take away the red underwear and put him in a darker blue, and that's all fine. Making him a newspaper reporter that wears an awesome hat in this day and age doesn't quite work anymore, and you have to work around that some, though its a huge part of the iconography. But that's all cosmetic and window dressing.
You can update and redefine presentation, bring in new stories and ideas... without messing up the tone and feel of the character, without betraying what the majority expect from him.
Nor 38% of the reviewers, apparently.
Referring to the Returns part, it does have a higher rating than MOS on RT (the reason we are talking about the reviews), so there's that.
It is okay to compare the movie to the old ones, but saying it isn't good because it is different is not okay, and a lot of the reviews are doing that. The movie should be judged on its story, dialogue, pacing, characterization, how well it adapts the comics, not based on what a 35 year old adaption did.