I sold my 2001 GTS ACR about a year ago. It was my daily driver for about 3 years.
The stock exhaust sounded very good, but keep in mind the 2001 had rear exhaust, so it sounds different from side exhaust. I changed to Bellanger headers, Random Tech high-flow cats, and Corsa 3" exhaust. Well worth the upgrade. It sounded fantastic - like what a Lamborghini would sound like all grown up.
I had it on a track twice. It tracks like a big car - very fast and predictable, but you feel like you are driving a fast station wagon.
Very comfortable car. At 70mph, it got 19mpg. Engine/trans/rear are nearly indestructible. Everything is overbuilt.
Maintenance is expensive unless you do everything yourself. I had a small
oil leak that is common on Vipers. The shop wanted something like $1,000 to repair. Even if you do the work yourself, parts are more expensive. Fortunately, they are pretty reliable.
Too much plastic on the dash. Some people address this with inserts or paint, but it looks stupid.
I love my CCX Cobra, but I miss my Viper. If I could swing it, I'd buy another. They are not expensive in the US. You can find Gen-2 Vipers in the $35K range all day long.