I want to keep things open to interpretation, but I can give a few examples.
For more generic things, something like, "This game looks buggy", "Was that supposed to happen?", "What the heck was that?", "Did they even test this thing?", or just simple exclamations like, "What", "Ugh", "No way", or anything of the sort.
For more specific things, just simple doubt or sarcasm could work, like, "Is he supposed to jump that high?", "It looks like he's floating", "So, are the spikes just for show?", and such.