My first 4runner was a 1999 4Runner which I gave to my brother (long story). Having driven that vehicle for two, trouble-free years, I decided to buy a used one to save money a little money to modify it to my liking. I purchased a 1998 in late 2001 and I'm just as happy if not happier with the 1998.
As others have said, reliability is the #1 reason why I purchased yet another 4runner. I've seen my brother's Isuzu Rodeo go down the drain into maintenance purgatory.
The quality, fit, and finish of the 4runner is outstanding. As it is one of the very few remaining Toyota vehicles still built in Japan, you know its been done right.
The exterior styling is classic, yet a little modern. It still looks like an SUV instead of these new current generation of poseur SUV body styles.
Interior styling is and was even back in 1998, dated. The center radio console is bland and the worst interior feature is the dash mounted cup holder.
Performance-wise, the 3.6L V6 is good enough for me. With a load of gear and 4 people though, the engine struggles slightly to get up 20 deg freeway inclines.
Off-road, it is highly capable unlike many of the pretenders out there like the national SUV sales leader, Ford Explorer.
Maintenance is easy on the 4runner. The commonality of the parts between the 4runner and Tacoma make it easy to find out advice from both communities. I'd say the most awkward basic maintenance item to change is getting out the oil filter, but if you go through the fender wheel well skirt, its not as big of a problem as say a mid-80's Nissan Maxima!