I just tried to bake some brown rice (350 degrees in a convection oven) in a white casserole dish that looks kind of like this. Anyway, after 30 minutes (what the recipe called for) it didn't work. The rice just sat there uncooked. So I dumped everything in a cast iron pot and got the job done. Why didn't the white dish work? The water was steaming when I took the dish out for the switch.
EDIT: the recipe called for 1 cup brown rice to 2.5 cups of water or low-sodium broth (I used water). This was same ratio on the rice's bag. Bake at 350F for 30-35 minutes. I did not put a lid on it for the casserole dish or the iron skillet.
Best Answer
This recipe should definitely work if you follow it correctly. Comparing your recipe to it might tell you what you did wrong. From the information you already gave, it seems certain that you didn't cook it long enough (as rumtscho said in the comments). Other things that could have been wrong:
Given your updates, well, basically I have no idea how that recipe would ever have worked. As you saw, the water wasn't even hot enough yet after half an hour. If you poured the water in boiling, it might have had a fighting chance, but it still would probably not have been long enough.
Cooking it uncovered is weird, too - it means that once it's hot, you'll start losing a lot of water to evaporation. The recipe on the bag likely has you cook it covered on the stove, so clearly you shouldn't be using the same amount of water with it uncovered.
As for the amount of water... 1:2.5 really sounds like too much water to me. I've seen some people online claiming that 1:2 is right for white rice, and brown rice needs more water, but in my experience that's a recipe for soggy, watery rice. (Edit: Of course I was basing that on covered rice; rumtscho rightly points out in the comments that for uncovered rice you'd need even more, since you lose some as I mentioned.)
So if I were you, I'd forget about the recipe you used, and try the one I linked to. Many people (including me) have had reliable success with it.