When I browse for new anime to watch, I can never help looking at the tags. Certain tags like vampire, school, or shounen immediately turn me away from a series because I know that most shows in those categories fall into trends I dislike. There are, of course, exceptions to these. I liked Kekkai Sensen, I liked Angel Beats, I liked Hunter x Hunter. But I've never found a genre so good and bad at the same time as romance.
So many anime have a problem with handling the romance genre in part because of the other genres the creators want to include in the show. Often, comedy-romances will have the main couple get together and break up every episode due to misunderstanding after misunderstanding. Part of what makes misunderstandings funny is that they rarely happen, but can lead to characters having coherent conversations about several disjoint topics at the same time. However, if all the characters are doing is talking past each other for four hours, stories don't progress, characters don't develop, and most importantly, I am bored. If the writers decide to include slice of life, they inhibit themselves to the slow everyday grind that doesn't make good television. Things might happen, but only around the 600 episode mark (wait--no Pokemon is more than 1000 epsiodes). The slice of life genre itself necessitates that nothing important happens, otherwise the writers might have to think about something like plot.
[gokai desu~]
The other part wrong with romance anime is the time period they choose to place their story. When all your characters are in high school, there's only a few themes your story can have, and those themes lose impact quick. Either it's a story about growing up and getting past crushes, about finding the one person right for you, or about the wacky hijinks of kids who will never find anyone. It doesn't help that the personalities given to the male characters for shows like this is dense as a brick and rejects all advances. Whenever something meaningful happens, the characters are either too flustered to do anything, or their reaction makes the other person too flustered. This isn't necessarily unrealistic so much as it doesn't make a good story. The best romance anime should work just as fine before and after the relationship starts. Any less proves that the whole point of the show was to see them get together. I've heard that Golden Time makes up for many of these flaws, but I've also been given plenty of reason not to watch it.
The best romance anime leave the beginning phase of the relationship as short as possible so the interesting characters can carry the plot themselves. Ironically enough, Sword Art Online handles this aspect fairly well. After going on some dates, Kirito and Asuna find that they're a good match, and I find the romantic scenes between them much more entertaining than the generic tsundere crap that happened early in season 1. Spice and Wolf would be my recommendation for someone who wants a good romance, but that's the only story I can think of that handles romance the way it should. Some other anime handle romance in an acceptable way, while still not being great. Shows like Sukasuka, Toradora, and Koe no Katachi are the best examples I can think of, so go give one of those a try.