My Dad's '99 Bonneville was a great car, although admittedly it was a rebadged/reskined version of the most of the other medium-large cars GM was making in the late 90s. He traded a '97 Oldmobile 88 for it, and aside from the more "aggresive" styling of the Pontiac exterior and the (slightly) sportier tuned engine and transmission, the two were quite similar. The interiors were nearly identical. The Buick LeSabres of the same age were effectively reskinned Olds 88s(as much as I love the Olds name and history, GM had let it flounder enough that it needed to go, as there was virtually no distinction between it and Buick).
I LOVED the G8. It's the same Holden Commodore that GM is now selling to the police market as the Chevy Caprice and the general market as the Chevy SS. This has proven to be a good, solid car. If I'm not mistaken, it's the only full size RWD Sedan that GM is making now(I'd class the CTS as closer to mid-size).
As per Wiki, the last generation GTO was the same Holden platform as the Cadillac Catera. The Catera was a car that got a lot of hate in the press at the time. My mom had a '99 that she bought in '02 or so, and I LOVED it. She got rid of it about the time I got my license so I didn't get a lot of wheel time with it, but it was a fun to drive and peppy car.