I'm obviously in the minority, but I think it sounds fine stock. You just have to get it out of your head that it needs to/should sound like a V8. I like the V8 sound, but I also think a lot of other engines sound good too. A wailing 1000cc sport bike sounds bad ass, I think my air-cooled 911 sounded awesome, a wound out 125cc 2 stroke sounds good to my ears, I loved my 300 hp outboard when it was maxed out on a tunnel hull that I had. My one bike had a 650cc single cylinder, I thought that sounded amazing with the right open exhaust.
The Raptor sounds like a turbo V6, which I think is fine. I don't expect it to sound like something else, just like I didn't expect my 911 to sound like a V8. I think it's fine that it has a pretty unique sound when I blast by someone.