Bfg only in space is quite difficult actually. If someone flies in air on the otherside of dm17, it's not that easy to hit him with bfg. Some bigger variations of dm17 makes it even more difficult. What makes it interesting is that you really need to aim and calculate from the great distance, where the enemy is going to land and to what direction he is going to fly. It's totally different game if you compare it to normal fight with all weapons. There is no rail or mg helping you.

What doesn't ever happen in bfg only is the incident when someone who masters some weapon like mg or rail just strafes on same spot and shoots the enemy down. It's not possible in bfg only. You need to be in constant movement even if you master the bfg.

I have played excessive ffa, freezetag and 1v1 for years and I think the bfg only on spacemaps is the only one where you really need to aim. Others you can just battle through. I think the rail only in space needs also aiming but it's boring because everytime you jump, you can concider yourself dead. So when you cut the jumping part out, only thing left is stalking and fast strafing = boring.

But as Shady said - guess it depends on people's taste.