I actually like Smash Up. But the way I go into it is treating it as a wild rumble, not a strategic or tactic optimizing game. It works if you accept to get tons of things wrong and have people play it with their guts, not their brains. Kinda like a card-game version of Wiz War. Just throw cards on the table and try to score and kill your opponent’s. I always make sure to teach new players aggression and attack right away, so they are not irritated when their plans are completely undone by someone else.
I can totally see people getting annoyed a d angry when playing it seriously, though. It is a really nasty game where you can get easily screwed by card draw and your opponent’s, where people can bang up on someone and where bash-the-leader is probably be the norm and not exception. It feels like munchkin, kinda. So I totally see it as failing in lots of groups and that is why I bring it to the table only rarely, because then it keeps it lightness for my group and doesn’t break the group.