The thing about kingdom come, the dark knight returns and watchmen is that so much of their narrative focus is on comics as a medium and superheroes as a genre, which makes them hard for new readers to "get"
If you choose to read watchmen, try to see each character as an analogue of a different superhero archetype but taken to the extreme. Also, one of the big themes is why people become superhefroes in the first place. Of all three it probably stands best in its own, but its still very much an insider's book IMO.
For DKR, you have to see it as the radical incarnation of batman that it was. While, at the time, batman wasn't Adam west-level cheesiness per-se, it was a lot brighter and much less niorish. TDKR reimagines batman as the character we know today, which his why some readers find it so underwhelming.
For KC, know that, in the 90's, comics were all about grim n gritty, mostly due to urge influence of DKR and watchmen.most of the superheroes were portrayed as amoral antiheroes, and KC is a critique of that
We3 was short and really good. Sandman is pretty awesome as well.