Simply so good! I nearly bawled my eyes out toward the end. It have its share of happiness, sadness, darkness, tears, etc.
The realistic situation is the driven force of this manga. Kain was afraid of someone finding out his sexuality and hides that fact of his sexual preferences. As the story goes on, we go through situations that are placed before Kain and Mel; like the meeting of Kain's parents, Mel's dark past, and the trama that Mel had to go through in the last 2 volumes.
The character development is a 10, given how sometimes petty fights or doubts can show what everyone's fears are deep inside; being that is they are being insecure or little doubts. Kain probably first came out as a playboy/jerk, but we slowly see that his devotion toward Mel was real and steadfast. Mel felt he was dirty and unworthy, and we see how he overcome his past (although some people probably won't agree with me with the "overcoming" part).
Storyplot is also a 10. Being that the manga first started in 1995, homosexuals were looked down upon and AIDS was referred to gay man disease way back then. The environment is the shaping force of this story.
Unfortnately, this manga not something smutty yaoi-fans would want to read. But I encourage you to keep an open mind and try to give this manga a try, so that you can at least have an idea of this gay couple's lifestyle and what they go through on the daily base when it comes to persecution, etc.