All vehicles have lemons. Every TJ lemon I've heard of has never had engine problems, it's usually everything else. However, it also depends on how people treat their vehicle, not many would come here to write a review and admit that they've really abused their vehicle with zero maintenance, then act surprised at its poor performance.
The Wrangler TJ is extremely reliable. If you're in the market for one, I would suggest you buy it. You won't have to worry about any maintenance issues except for routine work like oil changes etc. (given it's not a lemon, which most aren't). It will pay for itself by giving you thousands upon thousands of miles of driving.
It's extremely fun to drive, especially in the hot months when you can take the doors and top off.
The mileage is not great. If you put bigger tires on it then even more so. But for a 4x4 it's actually not bad, about average.
It's off-road capability is astounding. Out of the box, no other 4x4 comes close. Like they say: "Go anywhere, do anything"
That being said, the Wrangler is not for everyone. While it's a blast on-road and super capable off-road, everything else most people want out of a vehicle are not present in a Wrangler. It is NOT good at getting groceries, playing taxi or commuting. Depending on the model, it has either NO or FEW creature comforts. No power windows or locks. The ride is stiff and loud. Some have AC some don't. I don't need these things, I don't care about these things, but I acknowledge that most people do. In one sense, it is practical because it gets you from point A to point B with little maintenance and little regard for obstacles. On the other hand, it's not practical because that's all you can do with it... and at about 15mpg. With lots of low-end torque it CAN, however, tow very well.
However, the Wrangler (especially the TJ) has a HUGE aftermarket, allowing for some solutions to these problems (like sound proofing, storage etc.).
In the end, you have to ask yourself what kind of person you are. Like with most things, it's all personal preference. If all you care about is reliability, ease of maintenance (it's VERY easy to work on, simple design), on and off road capability, then this is the vehicle for you. If you want to haul people, go fast, or own an economical commuter, then look elsewhere.