The things I think are important in an anime are as following: Unique characters, intriguing story, good animation, originality and nice music.
5: Masterpieces, will never forget these animes. Definitely rewatchable and I would like everyone to watch them.
4,5: Awesome animes, will remember them for a long time.
4: Very cool animes, reccomendable.
3,5: Nice animes, enjoyed watching them.
3: OK animes.
2,5: Bad animes, lost interest while watching.
2: Really bad animes, definitely not worth watching.
Beneath 2 is utter crap, regret watching them.
The tags I generally like are: Action, Adventure, Comedy, Romance, Person in a strange world, Sports, Superpowers, Supernatural, Psychological, Coming of age, Shounen, Violence, Sci Fi, Samurai, Time travel, Feudal Japan, Swordplay, Drama and Mind games.