It was at its best in the OS, for Kanto and OI specifically, though Johto had an excellent English dub: 10/10
It went slightly downhill when Misty left but was still good in AG: 9/10
It went completely downhill when TPCi took over and ruined the English dub from BF to XY: 1/10
I couldn't disagree more with most of what natsulian7 said, by the way.
There is no stunning animation in the XY Series: Ash's eyes still look goofy, he doesn't even f*cking look his age (he's 10 for life!), and it's very overdone and exaggerated.
There is zero character development in XY Series apart from Clemont: Ash is as static and bland as ever, Bonnie is annoying and has zero depth to her character whatsoever, Serena has done nothing for 30+ episodes now but be a shallow, vain b*tch, there are no interactions: when do Bonnie and Ash EVER interact? Serena and Clemont? Never.
Overall: 1/10 because I hate what it's become-- 4Kids dubbed it a lot better over TPCi's garbage, and the older Series are better-- you want a real Pokemon Anime, watch "The Origin" or the OS or AG Series, not this trash.
If I could give it a lower rating, I WOULD: this is a TERRIBLE show now-- I would not recommend what it has to become to ANYONE.