Think of it as chocolate cake as opposed to chocolate ice cream. It may not be the ice cream you were expecting, but it's still chocolate. The movie made great use of the Victorian era setting. Rather than trying to cram exact replicas of Batman canon into the story and recycling existing lore, it reimagined the characters almost entirely to fit the plot, leaving the core premise of 'The Batman' intact. Some people may take issue with certain characters being so drastically different from their main timeline counterparts, but I personally find it to be refreshing. It's not the same old batman story we know and love, it's something else, and that's fine with me. TL;DR: Watch it with an open mind. If you take it for what it is, I think you'll enjoy quite a bit.
I understand that adaptions don't follow the source material exactly but they should at least include it. This adaption of the graphic novel didn't follow its source material hardly at all. Was disappointed that they made Gordon the killer instead of Bruce's uncle from London. Changing it to Gordon didn't make any sense at all. The only point they drew from the graphic novel was that that Bruce was accused of the crimes but even at the end, the movie doesn't show you how Bruce resolved that dilemma. He was still a convicted man who still needed to clear his name. If Gordon was the real killer, he died in the fire. His lab would be evidence but the movie closed out before we saw any of that. At least in the original story, Bruce caught the killer and then was able to show the GPD that it was his Uncle, not him, who was the Ripper. While I enjoyed the animation, music and voicework, I felt that they should have stuck closer to the source material.
I thought they did a great job converting the graphic novel into this animated movie. It was very different, but very much in the spirit of the elseworlds. The action was great, the story flowed, and the ending was tight, and we'll thought out. Just enough Easter eggs to make fun. However, not for kids. Which is fine, I don't think they wanted it to be.