Sounds like your brisket was moist and tender? Squishy is not necessarily a bad thing when it comes to a brisket flat. Most people seem to have more trouble with their flats coming out dry. A lot of the time people don't cook them to a high enough temperature, but sounds like 201 worked well. I usually go to about 195 in the flat, but I've had excellent results going to 200-205 too. I rarely trim the fat cap on flats. I don't find that the fat is usually that thick, and I would prefer that my guests decide whether they want to eat it or not on a slice by slice basis. If it's thicker than 3/8 inch, then you should trim it. Be careful not to overtrim though, because flats really need that fat cap. I also score the fat cap.
As far as flavor, you maybe just needed more salt. It's a big piece of meat, and you can put a good amount on it. Brining will help a lot with getting some salt into the meat. Or you can try a rub. Traditional Texas brisket is just salt and pepper, but I make my own rub for brisket with garlic powder, onion powder, paprika, chili powder, cumin, oregano, salt, pepper, brown sugar. I can post the amounts if you are interested. I'm pretty fond of my brisket rub. Leave the salt out of the rub (or reduce the amount) if you are brining.
