Without any modifications, my Beretta Cx4 Storm has been excellent. I couldn't help adding some upgrades.
I started with a good two point sling.
Next I added a barrel shroud. It was very easy to install and really works. That barrel gets hot! Damn hot.
The most notable addition is the EOTech 512. The EOTech 512.A65/1 is a Tactical HOLOgraphic weapon sight that actually runs on common AA Batteries. It works great but I wish it had a lower profile so that you could still see the fixed sights through.
--Big Mags and a Suppressor are what next!