Reliable - yes,
Use more fuel - yes, BUT not as much as people make out, they are much more efficient than people driving Big BMW's or V8 Land Cruisers in the that range of the big V's,
It won't burn a hole in your pocket, [only if you flog it, that's when you will know the difference]
If its been looked after, you will enjoy it,
I have a friend that has 2009 6L Calais, and he bought it new, and has L76 in it, and that is as smooth as silk to drive, NEVER been hammered, and is serviced regularly,
I have done a bit of work on it, and If I didn't have my 2002 L67 Calais,
I would definitely buy it off him when he goes to sell it, because its immaculate.
The good thing is that you can use E10 in it, which is a saving, but not sure about E85 for the 2009 model, where my L77 is E85 compatible, I did read that the Series 2 was the first to be E85 compatible,
where I use E85 when 91 or 95 ULP is up and down around $1.70 p/l, which it has been the past couple of weeks,
because E85 is approx. $1.45 p/l, but E85 doesn't last as long as std ULP, so its swings and roundabouts so to speak.
However, if it has AFM [Active Fuel management], you will save with that on the freeways and open roads,
Very smooth car to drive, when I purchased mine, and hasn't changed much since as I have looked after it,
It all boils down to, is it private sale, or a car yard, physical condition, does it have books from the previous owner/s, any history of it.
There is only one down side to the 2009 Series 1 model, the GPS [if it has that option], is not updateable, and if you can afford it, replace it with a Series 2 Radio/GPS IQ unit.
General Items to look for -
The Alternators usually fail at approx. 150,000 k's
Radiator fails at approx. 140,000 k's
Make sure 2 Belts [Alternator/Power Steering & Air Conditioning] are in good condition,
Good Battery
Front end not noisy
to mention a few, but they are normal items that you have on any car really,
But in a nut shell, they are a lovely car to drive.
Good luck.