Graduated Uni @ 20 and now professionally slacking!
My taste in Anime in general is... "more mature" to put it bluntly, but that doesn't mean I won't enjoy or rate highly the occasional mind-numbingly-mindless-hopelessly-entertaining series!
I find rating series to be a futile task because I'll recommend a series for a myriad of different reasons including: PURE BIAS (ghibli, music rich/focused), it was outstanding in one way (music, action, w/e), it was just too entertaining despite all its flaws (Geass), or it had some unforgettable, epic moments, some scene where the atmosphere, dialog, music, and feel just created something special.
As for ratings:
I won't rate anything above a 4.5 star (because nothing I've seen has been absolutely perfect, and I can't rate anything 4.999999999 stars!)
I wont rate anything below 2.5 stars
2.5 stars to me means: watch it if you have the time (it won't gouge your eyes out or melt your brain), otherwise you didn't miss anything special. Anything below 2.5 stars I stopped watching, attempted to purge from my memory, or won't admit to watching any of! (and so there probably wont be any series rated below 2.5!)