Well, the guy was an idiot. He read off a bunch of stuff, but had no knowledge.
The decklid would not open--or close. He removed the hump that allows engine clearance, and attached the spoiler to the quarter panels. The exhaust would make a mess on the sides. He cut down on the space to get in the door in the bottom (2"), back, and top. The windows won't go down all the way, and he made the interior 8 inches narrower. Those tires will make the ride very harsh. Due to seat placement, you'll lose leg room. That intake creates all sorts of issues. Where will the rear plate go? The exhaust layout causes all sorts of issues, being that high. The spoiler will sag terribly, and cause issues with the quarter panels. The trunk will leak. The rear lights will have to be very bright to be visible.
Even the MR2--which was toyota's johhny-come-lately copy of the Fiero--did not look that ugly. I think the MR2 looks very dated, and the exterior of the Fiero fairly modern.
I'm sure I could come up with more issues, if I thought about it.