The Flex's one major failing is that it just isn't very enjoyable to drive. Those used to SUVs will feel right at home with the Flex's truck-ish road feel, but you can do better.
Mazda's CX-9 comes close in size and could even be called fun to drive. GM's big crossovers -- the GMC Acadia, Saturn Outlook and the Buick Enclave -- drive more like cars than trucks, soaking up bumps while keeping an even keel in turns.
The Flex, by contrast, definitely feels like an SUV. The ride is somewhat stiff and the steering feels sluggish and remote. Handling through turns feels balanced, though, with well-controlled body lean, especially compared to a regular, truck-based SUV.
The Flex's 3.5-liter V6 engine provides ample power for driving around town. When pulling hard on the highway or when loaded down with people and luggage it starts to feel overworked and strained, though.
Next year, Ford will introduce a version with turbochargers and direct fuel injection. The extra power will be welcome and, hopefully, will be tuned to maintain something like this version's fuel economy numbers.