I think when 'plastic' aircraft are all shiny and new, they are definitely better than traditional metal aircraft (lighter, stronger, fatigue & corrosion resistant, more complex shapes) but their main problem is, as Ultralights mentioned, the NDT. It's a lot harder and requires more specialized tools and training to firstly identify the damage and then to repair it. It will be interesting to see how well the composite airframes are doing 10-15 years down the track, after a bit of use and abuse.