A friend has just bought a very nice GTS and having driven it I have to agree with Stuart.
That said I think the Quattroporte is one of the best looking large saloons to have been produced and I much prefer it to the current version together with a lot of the competition. The interiors are stylish and are a very special place to be with plenty of space. I was surprised by how small the boot was for a car of this size - It would rule one out for me purely from a practical perspective (probably a reflection of the front/mid engine setup). But they are fun to drive for such a large car, with light communicative steering, and I could listen to the roar from the engine at higher revs all day (gave me goose bumps!! - just brilliant). However imo they are just not as agile as the smaller saloons and the brakes and engine torque were less impressive when compared with the ISF. It very much depends on what your priorities are and for me they are just not dynamic enough.
My friend had an E46 M3 before and was tired of the firm ride on our less than perfect roads. He loves the Maserati and I can totally see why. That said he has already had an issue with the CD player not working, which to be fair may equally be due to the age of the car. I just hope this car doesn't prove as unreliable as Maserati's of old because he will need very deep pockets to keep it running from what he has told me!!.
We all buy cars based on our own preferences so go and drive one (if you haven't already) because its a great car. I'm sure you will enjoy the experience whether you decide to buy one or not!! Let us know what you decide and what you think of the car.