Personally, I don't have any complaints... but I can list the ones I have heard:
1. Forearm Rattle - This is the biggest complaint (solved by tightening two allen screws on the forearm).
2. Look - People don't care for the look.
3. Misfires - Some guy on here continually claims that he knows of two Novas that don't fire on the first (or second) shell. However, I'd have to say he is in a vast minority. I haven't heard of any other misfires with properly maintained Nova's. Quite the opposite, infact.
4. Trigger - Someone around here loves to complain about "horrible" trigger on the Nova. I'll say it again... it's on level with any guns in that price-range. Not something unique to the Nova at all.
That about sums up the complaints I have heard. Oh yeah, it is not American-made. However, if you are desperate, you can use it to dig a fox-hole against the Italians. So, stuff that argument.
