GW and
FW resins have plenty of faults, but I've never had a prob with gluing them to plastic or each other. Yes you need to use super glue, so no it doesn't melt the pieces together like plastics. But generally the pieces will stick together pretty well.
If its a larger model, then I'd recommend pinning. But that good advice regardless of material.
Pieces like
FW doors tend to be small than the
GW doors they intend to replace, so sometimes fit is a little tricky.
Warped pieces are easily fixed by putting them in warm water, or even using a hair dryer on them for 20 seconds.
Thin spots, pin holes, air bubles, miscasts.. That depends on your ability or willingness to use green stuff / putty.
I personally never had a
FW model or Finecrap I couldn't work with.