Sorry for the long post...
Gen7 models range in years from 2008 to 2012. Here are some things to know that will help you decide what to ask about:
2008 and 2009, and possibly some 2010, models with the 6-speed may have an issue with the 3-5-R Wave Plate. The early versions seemed to fail at an accelerated rate. Check the VIN at a dealer to see if the recall was ever done.
Early Gen7 models offered 3 engines: 2.4L I4, 3.5L V6 (pushrod), 3.6L V6 (DOHC). The 3.6L in my 2009 was mated with the 6-speed automatic, whereas the 2.4L got the 4-speed. In later years, the 6-speed replaced the 4-speed as the only option. I'm not 100% sure, but I believe the 3.5L was available only with the 4-speed.
There were 2 types of power steering: hydraulic and electronic. The 3.6L got hydraulic and the 2.4L got EPS. There are some issues with the EPS that some hate and others are only mildly bothered with. Overall, EPS requires less effort by the driver to turn the wheel compared to hydraulic.
The 3.5L pushrod was a carry-over engine that was fairly sturdy and bullet-proof, being used mostly in fleet orders: taxi, rental, etc.
The 3.6L was the only engine with a factory "dual" exhaust. The other 2 engines both came with single exhaust. I put "dual" in quotes because it's not a dual exhaust like the cars of yesteryear. It uses a single pipe all the way to the back where it enters the muffler. Only then does it exit the muffler as 2 pipes. It looks more symmetrical but otherwise it probably provides very little extra performance.
Changing the headlights requires removal of the bumper cover. For some it can take longer to remove it than it takes to do the bulbs, and they still need to put it back on. There are videos on the interwebby with ideas on how to speed it along.
The gas pedal is wired to the computer rather than being a mechanical connection to the throttle body.
The 6-speed transmission came with the ability to put it in either D or M modes for forward movement. D is the usual fully-automatic drive mode. M is the manually-selected mode. More correctly, you don't "select" the gear, you "request" it from the computer. When in M at a stop, you can start in either 1, 2, or 3 with the V6 (1 or 2 with the I4). Once underway, selecting "+" will request an upshift, but it won't happen if doing so would make the engine slow too much. Selecting "-" will request a downshift, but it won't happen if doing so would make the engine go too fast. In either case, shifting is accomplished using torque management. Because the gas pedal is wired, TM will reduce the amount of throttle being applied, perform the shift, then reapply the throttle based on the pedal input. TM helps to reduce stresses on the transmission, but the cost is a little more clutch wear. Using software such as HP Tuners (there may be others), you can modify a number of parameters, not the least of which is the shift tables and TM. In my 3.6L, my TM is turned completely off.
Additionally, when using Cruise Control, the stock shifting strategy allows the car to lose more speed than usual when going uphill, often forcing a downshift from 6 to 4 instead of 6 to 5. This kills MPGs and makes for an annoying trip. My CC tables were also altered and now CC on trips is much more responsive!
The radio uses dot matrix technology. It sounds fine for most listeners. Some members have replaced theirs with 7" or 8" screens and they look really nice.
The turn signal blink sound is fake. It is produced by the computer and sent to the left front speaker. The alert chimes also come from front left.
If the vehicle has Blue Tooth, you can make/take calls hands-free using buttons on the steering wheel, and even possibly use voice commands to find and dial your number.
The computer controls many things, including the exterior lights.
LTZ models come with special stop/turn/tail light housings that take a special Philips Joule LED bulb. The housings use a clear outer cover, making them appear "white". The LED creates red light at 2 levels: running and stop/turn. The cadence is controlled by the computer as well. If you have a non-LTZ with red housings and want the clear ones, you'll need to get the housings, the LED bulbs, and the harness that goes from the rear fuse box to the lights. The bulbs are not interchangeable between housings. Changing from regular to LED bulbs will cause the computer to get all mixed up and produce a weird cadence for the LEDs, but it can be overcome or you can just live with it.
The headlights use halogens in a non-projector housing. H9 for highs, H11 for lows. There are HID bulbs available that will replace the halogens, but most who've tried them have reported light spraying all over the place. There are also LEDs available. I've tried 2 kinds. The first was a single COB version that didn't work as well as it could have. The second, which is currently installed, uses 3 very small LEDs on each side of a thin PC board and does quite well. They are brighter and better than the halogens, but the halogens were way better than the old sealed beams from years ago, so consider what could have been and then decide for yourself.
Early Gen7 models suffered from the door latch/lock mechanism (all in one) failing prematurely. A number of new versions came out, and by 2010 or 2011 they seemed to get them sorted out. There is a thread about bypassing the failed lock function with an external aftermarket solenoid/motor that can be retrofitted. The cost for 4 is around $50 and can be done by most DIYers.
Some of the early Gen7 models suffered from the driver's seat frame having a weld fail, causing the seat to feel like it was tipping, and making it so that certain adjustments could not be made. Later models have not been reported to have this issue AFAIK.
Early models (2008-09) required only conventional motor oil to meet warranty specs. 2010 and newer required a synthetic blend meeting a new "dexos1" spec that is unique to GM. Using fully synthetic motor oil exceeds those specs in most cases. Check your requirements and the oil specs to decide what you feel is best.
The 3.6L is a great engine and has only one Achilles' Heel: the DOHC set-up has 3 timing chains and 7 chain tensioners. The tensioners use plastic linings to contact the chain. A number of comments have been made regarding oil change intervals and/or oil type contributing to increased wear of the plastic linings. A good regimen of regular oil changes with quality oil should help extend their lives. I use a fully synthetic oil rated to go 25K miles but I usually change it at around 5ooo miles. A couple of times I caught myself forgetting and went 7ooo miles.
On my 3.6L, I used a kit to move the spin-on oil filter location from the side of the block at a 45° angle to another spot where it is completely vertical. This does several things: 1) it no longer requires me to remove the air intake tube to reach the filter, 2) I no longer have to be close to the exhaust when accessing the filter, 3) removing the filter no longer drips oil all over electrical wiring and doesn't spill on the ground, 4) instead of the stock size of a tiny teacup filter, it now uses one that is over 2x the size, so I feel that it will filter better due to having more area of media, which allows it to more more slowly to capture impurities better. I have a thread about it if you are interested in finding it.
A few members have reported water leaks with the sunroof due to one or more of the drain hoses becoming disconnected. It caused water in the floorboards and sometimes stains on the headliner. The simplest fix has been to get a short piece of tubing and extend the hose connections.
Overall, I consider the Gen7 to be a fairly decent car. I'm on my 3rd one as of this writing. The first was a 2009 2LT with 3.6L V6, traded at 20K miles. The second was a 2011 LTZ with 3.6L V6, lost to a flood after 3 years at only 44K miles. The third (current) is a 2011 3.6L V6. At 94,ooo miles the engine was replaced after a connecting rod broke and punched a hole in the bottom of the oil pan and another through the side of the block. The Power Train warranty took care of everything, and I was so glad that it did! I treat this engine better than I ever did the other two!
The 2.4L is a very strong engine for its size. It compares well with larger straight sixes of older cars and does a venerable job of moving a car with a curb weight well above 3200 pounds. The 3.6L compares well with older small-block V8s, as does the 3.5L but with only a few less HP.