I've owned a Gen 2, two Gen 3s, and now two Gen 4s. I've also recently driven a Gen 5 (SRT not a GTS) for a bit over 100 miles. Here's what I like about the Gen 5:
1) Fit and finish of the exterior is simply superior to any previous Gen car. However, see dislikes below.
2) Interior is waaaaay better than any previous Gen car.
3) Stereo sounds great even in the SRT. I understand the GTS is even better.
4) Cruise control.
5) Electronic gauges - truly great.
6) Performance, this thing moves.
7) Exhaust note, except as noted below.
8) Rear end design is nice. **** actually.
9) Wheels are nice.
10) Rear tires are reallllllllly wide!
11) Window swtiches return to the doors.
12) The ride is much better than any previous gen car. Feels solid.
Things I didn't like:
1) I could not get comfortable in the seats no matter what I did. The owner of the particular car I drove echoed this sentiment. After 100 miles on the interstate my back hurt.
2) The hood vents look cheap, should have been stainless steel mesh or something more exotic.
3) Grille looks cheap and seems pretty flimsy. I think it would look better in body color too.
4) Gearing isn't to my liking. I live in CO and the distances out here are vast and the speed limits high. At 80mph the Gen 5 was revving much higher than my Gen 4 even in 6th. Exhaust note, while pleasant at lower rpms got tiring at 2300RPMs.
5) I don't like the front end design although this might be improved if the grille was body color (IMO).
6) Auto dimmiing mirror that has no off switch. I never dim my mirror, my eyes need all the light they can get. You simply should be able to turn the auto dimming feature off.
7) Other than Stryker Red, they need more in your face colors (SSG, VBB, VVO, whatever).
8) Front of car really hard to see. Where does the hood end? I suppose I'd get used to this.
9) No vert or ACR yet although you can see if you open rear hatch that it is already designed to accept a wing.
10) No glove box, or did I not see it??
There were probably a few other items in both lists but that's what I most remember.