Brussels are one of those brassicas that are difficult to grow well first time, unless you have the perfect ground and are lucky.
Blown sprouts are a sign of them being under stress from quite a few issues, from being blown around in the wind, lack of water, being attacked badly by pests, to not having the right nutrients, especially nitrogen.
You can eat the blown sprouts no problem, very tasty, but not why we all grow them of course. Maybe you could give them some BFB or chicken pellets and give them a good soaking, and the later sprouts might hold their shape, but it's likely now most of them will also blow somewhat and/or be quite small, but you never know. No matter, we all double our efforts and make sure we do better next year.
I had terrible brussels three years ago when I first gave them a go after being badgered relentlessly to grow them. Last year was only a little better, so I really concentrated on them this year, especially making sure the bed was as perfect as I could make it. And it's worked. This year, they're fantastic so far, and look like they'll be the real Mccoy. I have cheated a little in my mind by growing an F1 variety, but it's helped.
Some plants will grow reasonably well with little effort. Brussels need the right conditions to grow like the shop veg. They like a bed that supplies good amounts of water, loads of nitrogen, a very firm soil, and a good start in life in their pots. And a very good netting to keep the early pests at bay. My bed also got a big manuring in the Autumn, limed a little in the Spring, and a large dressing of chicken manure just before planting. Classic brassica prep.