5th gen camry 4cyl has random issues with loose head bolts leading to head gasket trouble

6th gen had LOTS of issues initially, like leaky VVTi oil lines, bad transmission/ECU programming, SUA issues (mats, brake pedals, no brake override in ECU programming, etc)
worth mentioning that both gen5&6 are interference engines, so if the timing gets by any chance screwed up that's it for the engine (gets damaged). on the other hand timing chains last pretty much the life of car.
3rd & 4th gen are pretty neat (4th gen calls for more frequent oil changes though due to lack of oil cooler). all cars require maintenance though, if you are not willing to do that then stick to mass transit and forget about cars.