You could ask 50 people and you will get 50 different answers. For myself as a kid in the 80's it was the ultimate freedom as for some reason I wanted to feel like I could fly. So when I saw people jumping their BMX's I automatically wanted to do that to. As a adult I still have that feeling and I enjoy riding BMX because I don't get bored trying to challenge myself.
I can tell you what attracted me to my first BMX. As a kid I grew up poor and had a banana seat bike. I wanted a BMX so bad I went out and got a paper route. I went to the bike shop and there it was...I didn't know a single thing about BMX, but just about every part of the bike was beautifully chromed. It was a used GT Pro Freestyle Tour. And it seemed so much cooler and nicer then the other bikes. It was $350cdn and I only made $30/month on my paper route but the kind bike shop owner let me pay it off at $30 month for a year. Later I found out that I had bought a freestyle bike and it wasn't really suited for racing but that was OK.
With your Brother there are many things we need to know.
Does he already ride bmx, and how old is he? . Does he want to race, or just cruise around?