I'm with everyone else so far - every woman, and every pregnancy, is different. It all depends on so many different things that it's impossible to say what is 'good' and what is 'bad' - each case has to be judged on its own merit.
I personally have done both 'extremes' - I started out underweight (for my height, I'm really tall) when I fell pregnant with DD1, and by the time I gave birth I'd put on 30kgs (although I had really excessive amniotic fluid which was worth around twice as much as 'average', and got fluid retention towards the end which added to the numbers on the scales)!!
I lost 15kgs after having her and am within the healthy weight range for my height, and I'm now 25 weeks pregnant and have only put on 4 kilos (which I keep gaining and losing, gaining and losing, I've just lost it all again because I've been sick for two weeks with the flu and haven't been eating). I keep worrying about it but my doctor assures me the baby's 'eating' all my love handles and although it looks like I'm losing weight (I've lost a dress size and my upper arms are definitely slimmer than usual), the baby is taking all that and using it for itself, so there's nothing unusual about it, or anything to worry about. My gut is *huge*, so obviously something's growing perfectly normally in there!!

Don't panic, my doctor has told me anything from 8kgs to 30kgs is 'normal' depending on factors like your weight to begin with etc. As long as your GP says bub is growing normally and healthily, keep on doing whatever you're doing