I liked Cruel Romance, but thought Too Late to Say I Love You was much better written in terms of character development and the general theme of loving unselfishly that ran throughout the drama.
Cruel Romance featured a fairy tale like type of love story, which is good for a few hours of relaxation and escape, but Too Late felt more real and believable, like this is a story that could have happened in real life. In fact, I believe I read somewhere that the story was, indeed, loosely based on the life of a real life General.
I loved that the characters in Too Late weren't noble idiots (at least for a large portion of the drama). They didn't always stick to the strict moral codes of Chinese society, something I have never, ever seen in any Asian drama. Usually the characters behave like martyrs, always putting other people's needs, expectations and opinions above their own in a way that doesn't rhyme with logical behaviour, all because the writers want to portray the characters as pillars of morality, esp when it comes to the female leads. If you're a good, decent person, then you must sacrifice yourself, your own happiness at all times etc.
In Too Late, this wasn't the case, the characters pursued their own wants and needs, sometimes without thought for what other people think or what dangers may lie ahead. This was in fact a complaint of some people who watched this drama -- they believe 'A war is going on, how can these people behave this way? It's not believable!' but it was totally believable for me. Why? Because love is an incredibly, powerful drug that can drive otherwise rational, objective people to make irrational decisions. Wars and other conflict have been started because of love. So to me they acted according to human nature -- which is largely self-serving. Noble idiots really piss me off with their very fake sense of morality and self-righteousness. I like when characters behave like human beings, when they make mistakes and learn from them.
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As I mentioned I haven't seen Battle of Changsha yet and I will wait to watch it because a drama with just pure death and misery is not really my cup of tea, unless I have a mood for it. I personally prefer shows like Too Late, where romance is the focus and the backdrop of war and or other crisis situations is used to heighten the emotion and palpability of the characters' feelings for each other. And Too Late is just right for that. The romance was mature and relatable and full of passion, just the way I like it. Therefore, if you like the same, then Too Late (and to a lesser extent Cruel Romance) are both very good dramas. I don't think it's fair to compare their 'goodness' to Battle of Changsha because that drama is in a completely different genre, with a completely different focus and outcome.
The only disadvantage with both dramas are the endings. The ending of Cruel Romance felt a little bit rushed and abrupt to me, which lessened the impact of the show overall. For Too Late, the drama was a 10 up until around episode 23 - 25, after that things kind of took a less than satisfying turn and I reduced my rating to around 8/8.5. The ending, the payoff of having investigated your time, could have absolutely been better. Having said that, even with the somewhat poor ending, if you like this type of drama then it should not be missed.
I know you're specifically looking for war dramas, but I'm just putting this out there for others who might be interested to watch these dramas.