I recently got a 348. Here are a few of my early impressions:
There's no comparing the 348 with the NSX in terms of materials, fit or finish. The shifting is notchy, the clutch, steering and suspension are heavier. It makes a few more rattles and the windows take their time reaching their destination. The chassis isn't as stiff despite the car being heavier overall, (although to be fair I got the TS version). By most objective measures the 348 isn't up to the standards set by the NSX.
Despite all this the car is magic. It sounds and looks fantastic. It has a wonderful raw feel to it...like you're more connected to the machine and the road. And it's natural for car guys (and gals) to feel good about owning a Ferrari, they have a very special history...much of it still being written every race weekend.
In summary it's not as good a car... but it can be just as rewarding.
Caveat: Both my NSX and 348 are recreational use. I could imagine the NSX as a daily driver, I think the 348 would have a harder time playing that role.