All Renault brakes work very well, they are self adjusting except for the handbrake.
There is no way you or a mechanic can adjust how sharp the foot brake is.
You could also have "brake assist" on your Renault, if you hit the brake pedal fast, as in an emergency the "brake assist" will put the brakes full on for you and the ABS will operate.
sleepyj, what did you drive before you got the scenic? I remember the first car I got with "decent modern brakes" on it and how I spent some time nearly putting myself through the windscreen every time I hit the brakes.
Do you drive it everyday, I have an old Ford and I only use it at weekends and when I drive it after leaving it for the week the brakes are very sharp for the first mile or so then they are all ok....