My favourite genre used to be romance, but I find that I've watched so many romances now that I end up giving most new shows low ratings. It's hard when you are too familiar with the genre clichés. So nowadays my favourite series seem to be slice of life, preferably with salarymen or at least with adult characters, drama rather than comedy. Maybe it's been too long since my high school days. My order of preference would probably be Josei > Seinen > Shojo > Shonen but I do watch several genres.
In my ratings 5 is an average show that either has too many clichés or some serious flaws. I'd say that a 5 anime is still enjoyable to watch, but something I wouldn't have regretted not seeing. Anything above that is worth seeing. Not every anime can be a masterpiece but sometimes it's fun to watch some fluff without depth. I do tend to be harder on series that set up high expectations in the beginning but fail to deliver in the end. And I don't give the series a high rating just because it has a great ending.