Generally thumbs-up is a sign of approval, and thumbs-down is a sign of disapproval, similar to a smile or a frown respectively.
In any case, I generally judge decks by a few metrics.
First, see how much thought went into the deck. If it is just an oraclebow that ignores the oraclecard, probably not much thought. Same with a standard firestall or immorush. An example contrary just today are a rainbow that depended heavily on the death aspect, vultures, lots of mass CC, cats, a graveyard... and pulvy to take care of the PC half. As for the immorush, I generally agree, if it is used just as an aggro enhancer I'm fine with it, for example if you actually throw in some rainbow towers to enhance the rainbow aspect and turn it into a half/firerush half rainbow.
Next is the league they are in. I know I've thumbs-upped a deck in gold that I wouldn't have in plat, simply because in gold its not expected of them to have every card imaginable. Also, its a lot rougher there to stay afloat with the increased player base + decreased points to buff the decks.
But as to the original post, I never thumbs-down a deck merely because it frustrates me, partly because I know that had I picked a different farmer I'd have probably crushed it like a pancake unless it was one of the big 'staple' decks anyway. And even 'those' have decks that obliterate them, decks that actually work against a wide variety of decks.
SoSa - 500 HP EM deck, purple nymph heavy anti-matter, A deck that combines Purify + Eternity.
Firestall - Not even that strong anymore, but SoR Pharaoh, Defensive CCYB, Disc-Hole.
Ghostmare - SoR Pharaoh, Ghostmare sometimes, purple nymph anti-matter, sometimes Disc-Hole.
Mono-Aether - Mono-Gravity, Defensive CCYB with Pulvy, sometimes Disc-Hole.
So if I lose a match in this manner, its usually because I mis-read the metagame or an accepted loss to beat the usual metagame, not because I 'had' to lose. Granted SoSa is the hardest to deal with, but even it can be beaten, and its actually not prevalent enough to warrant switching to a deck that does. I mainly 'do' take issue with Arena SoSa though because by itself it 'will' win games, even if the entire rest of the deck is 100% neutered. I remember losing to a deck that played literally nothing 'but' SoSa, chance it was supposed to be a farm though. But if I ever get 'that' bothered by it I'll just throw an eternity into a deck with some healing and call it a day.