Darn, mine's an '03.
5 cylinders are A-OK, they balance properly and all that. It's just a space-saving measure. Modern engines control fuel burn better with smaller cylinders, and since they had an engine already with decent emissions and mileage but had 6 cylinders and needed a four, they dropped one, because dropping two would have made it *too* small while using the same cylinders, rods, etc.
I read a long article about it a year or two ago when those new engines came out. Decent motors, too, as well as the 2.2 Ecotec, very overbuilt. Seems the tuner crowd (the real ones, not the Nawz Kiddiez) got a stock one to make 350HP with no issues, asides from the added turbocharger.