Very reliable truck. I have 120k miles on the truck and the only serious malfunction I've had is the a.c. compressor failed prematurely. I have also replaced the knock sensor and have done a preventative timing belt change. Starts every time and does everything your ask from a small truck including towing without incident. Truck isn't particularly fast and it gets 17 mpg mixed driving but it's a truck so that's ok. Bought this instead of a Tacoma and I've had no regrets.
I have owned this truck since new and it has been a very reliable vehicle. The acceleration is not very good and the back seats are fairly cramped for the average adult ,but fine for kids. The mpg is also very average. I know some full size truck owners who probably get as good MPG with more space. The rear doors also do not open up wide enough(only about 45 degrees). However, having said all that, this truck has been rock solid in terms of reliability and that is important to most people. The truck is a 5 passenger vehicle and it does have a 6 foot bed. The truck is very good in the snow. Tires, brakes, and basic maintenance like oil changes, air filters, transmission flush, etc are the only things I've had done. I would say the truck was a very good value for the dollar at the time when bought brand new in 2004 which included the roof rack(which comes in handy), power windows, power door locks, cruise control, bed liner,and cd player. I would not hesitate to buy a used frontier if the previous owner took decent care of it.