Fun start to the week! Four items that can be CAST to start off the theme answers - a net, a play, a spell, and a shadow. Lovely.
I like seeing NETNEUTRALITY in the grid. It's sad that it's a topic of debate at all, and in all likelihood, it will soon only be remembered with nostalgia. PLAYPOSSUM is certainly a familiar expression, but when's the last time you said it? SPELLCHECK is a blessing and a curse (well, I guess autocorrect is really the curse part), and as for SHADOWCABINET (Opposition party group in British politics), I've heard of it, but I'd be hard pressed to explain it.
TALENTSHOW and SEEYALATER are nice as bonus long fill, and don't you think LEGALID should become a new word meaning "legal id?" It would be pronounced like "eyelid," but with one more syllable.
STINKO (Drunk, in dated slang) is a word GROUCHO might have used, and ETAPE (French word for a leg of the Tour de France) seems a little récherché for a Monday, but all in all, I thought this was a solid start to the week.