Your first problem is trying to use iTunes to edit video metadata. Save yourself the hassle and use a 3rd party program that knocks everything out in one fell swoop. I use MP4Tools for 95% of conversion I need done, Handbrake for stuff that actually needs full-blown conversion, then I dump it into iVI which I use only to edit the metadata (Info Only conversion mode) as I've not been even close to impressed with it's ability as a converter, but it's pretty solid for metadata. I get TV show artwork here:
http://iart.toaos.tk
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Also, I haven't used iTunes 12 since swapping out my 2013 rMBP for the 2014 rMBP, but have they done anything to make it easier to switch between Songs, Artists, and Albums views in the music section? I hate that it's a drop down now. I tried finding keyboard shortcuts but wasn't able to figure that out. Frustrating.
Many of the iTunes 11 bugs, particularly in search, seemed sorted out in 12, so I was generally happy with the update relative to how excited anyone can get over an iTunes update these days. I think the program gets a bit more flack than it deserves, but it's long been one of the weaker, buggier applications from Apple.