Everyone who points it out is absolutely, one hundred percent correct. Nothing the TARDIS does in this episode makes any sense. If you're trying to warn people that there's a stuck switch that they need to fix, melting all the clock-faces and knocking them unconscious and rendering them half-crazed with concussions and flashing random lights and showing random pictures on the scanner and electrifying most of the console is not the way to go about it if you have any kind of common sense at all. The big twist of the episode is that the TARDIS is intelligent, but it's rubbish at communicating.
But isn't that exactly what makes this concept work? The TARDIS is intelligent, yes. But it's not intelligent like you or I are intelligent. It is not a human. Ironically, Barbara had it right in the very beginning--there is a strange, alien intelligence inside the TARDIS. It's just that it's the TARDIS.
In that light, the weird and shambolic attempts to communicate are strangely brilliant script-writing. They convey just how alien the TARDIS is; simply attempting to communicate with the crew drives them to the edge of madness. Just describing a stuck switch can only be done in the loosest, most symbolic terms, by a creature who barely understands linear concepts of time let alone such human constructs as language. Idris might have gotten her tenses mixed up, but her human body brought her closer to the way the Doctor thinks than she'd ever been. And watching "The Brink of Disaster" shows that clearly.
Of course, I can't discuss an episode at this stage of the program's history without gushing over the chemistry between the four regulars, and this is no exception. The scene between the Doctor and Ian, where he explains that he lied about the amount of time remaining to them so that the others won't die in fear, is a wonderful piece of bonding between the two characters. It makes the subsequent scene, where the Doctor struggles to swallow his pride and apologize to Ian and Ian lets him squirm for just a moment before letting him off the hook, work that much better. This whole episode is really a turning point for the regulars, in fact. The final sequence between the Doctor and Barbara (and really, I can't imagine this scene working for any other set of actors in the show's long history) is a magnificent piece of characterization.
It's also quite necessary. As much as the semi-antagonistic relationship has created some amazing tension, it has to break at some point. The four leads can't spend forever at each other's throats, not without the story degenerating into pure antagonism. They're learning to trust each other, and you know what? It's the perfect time for that to happen. Ian, Susan, Barbara and the Doctor are about to start their real adventures, as a real TARDIS crew. And this two-parter--a crisis affecting only the four of them, that they could resolve only as a team--was exactly what was needed to make it happen.