I see this chapter as a microcosm of the series as a whole. We start off the chapter with the mundane topic of exams, something pretty much everyone can relate to, much like each book starts off with Harry in the muggle world. Even the magic that is done is the exams seems a bit ordinary.
Juxtapose that banality with what happens when they go through the trapdoor (does anyone else see an Alice reference here?). Their lives are immediately put into danger when the Devil's Snare attacks and things get progressively more dangerous as they make their way through the chambers to find Snape. Similarly, the danger grows throughout the series, until you reach the bloodbath of Deathly Hallows.
We also get an advance look at the friendship between Harry, Ron, and Hermione as we see for the first time just how strong the bond between them is. Not only do Ron and Hermione accompany Harry into danger, they do it without thought. It's striking that here Ron doesn't even consult with Hermione before saying that they're going with Harry, much as Hermione doesn't consult with Ron at the end of Half Blood Prince before saying they're joining him in the Horcrux hung. Furthermore, we see just how far they are willing to take things when Ron sacrifices himself in the chess match. Both are aware from an early point how dangerous being friends with Harry can be, and neither one cares. The power of love is the overarching theme of the series, and Ron and Hermione exemplify it here.
Now, that I've gotten all the academic stuff out of the way, a few quick, fun points. I've found that it is physically impossible for me to read the Snape line "people will think you're up to something" without pausing between "you're" and "up", I couldn't even type it just now without pausing! I'd also be remiss if I didn't at least mention the first of the bookend "ARE YOU A WITCH OR AREN'T YOU?", consider it mentioned. Finally, I'm curious to know what everyone's favorite enchantment is? I'm partial to Snape's myself, which I imagine stems from my dad teaching me logic puzzles from a young age, I just find it frustrating that it doesn't give us a picture of the bottles so we could try to figure it out for ourselves before reading Hermione's answer!