It was pretty nasty: 10 cm wide - the whole damn kneecap covering, pretty much, but thankfully no muscles or tendons were severed so no crippling will result, just scarring. Fortunately it happened at 1 AM ish, so the roads were clear and emergency was pretty slow and I was back home by 4. I felt bad about depriving my mom of sleep, but it was an interesting experience, from the panicked "oh shit" reaction (a mix of rational "gotta go to wake up mom to drive me to the hospital and get stitches" to the irrational "must hold the skin together by hand since if I let it stay separated for even one minute it'll clot down there and never heal properly!!11!!"), to the adrenaline rush that got me up the stairs to wake up my parents (a mix of profanity, moaning and apologies for the inconvenience), to the low blood pressure crash that followed (dunno how low it went, but I probably would have fainted or had temporarily blindness had I not been sitting on the floor already, and by the time I got to the Emergency room it was only up to 60/40 - I was apparently white as a ghost), to getting wheeled around on a stretcher, to watching the stitching process itself (never had to get them before - reminds me of sewing up a net at my bird research job, but gorier).
My mom and I forgot to bring books, tho, so there was also a lot of boring waiting around and making idle chit-chat too. For a gaping hole, it didn't actually hurt too terribly much (despite also forgetting to take any painkillers) or bleed that excessively: it stung more than anything else, like a fire ant bite, and wiggling my toes helped keep it under control, although once they started washing out the wound, that hurt (couldn't stop the leg from tensing up and shuddering) and the freezing didn't take everywhere - but even then the stitching was no worse than any old needle (and the really ravaged chunk of skin did go numb, at least). Now my leg's just achy since I can't bend it too much; a little cut I also got on the bottom of my other foot's heel at the same time is actually much more painful now for walking on - gotta go digitigrade for the time being. And try to minimize stair climbing, ugh, so tedious.
EDIT: Spoke too soon - the knee's starting to sting again, argh.