We just replaced the tires. The were the O/E BF Goodrich tires, so I'd say that three years out of them was good enough. We live in Colorado and venture into the mountains most winters, so we opted to put on wider tires. We chose BF Goodrich Long Trail TAs in 275-60-R17, and while they aren't any taller than stock, the wider footprint makes the Explorer look very good compared to the originals (which were 255-60-R17 if I remember correctly).
Other than that, just general maintenance. No major problems whatsoever.
We have an 03 Eddie Bauer that I bought for my wife, and it is a very roomy ride compared to my '99 GMC Envoy. I have a few things that I don't care for - some are minor annoyances and some are personal preference. Overall this has been a great vehicle.
1. The seats. The leather looks excellent after three years, and the heaters are very nice, but they aren't very plush compared to those in my '99 GMC Envoy or my '02 Grand Prix GTP - those seats are MUCH more comfortable, in my opinion. That's just a GM vs. Ford preference thing though, I think.
2. The Door Adjar indicator has a mind of it's own sometimes... we can shut and re-check all of the doors three times, but the indicator doesn't go away. It takes about 30 seconds for the interior lights to shut off if that indicator is on. No big deal most of the time, except at night. Driving with the lights on is rather annoying. I'd chalk this one up to a poor design on Ford's part.
3. There is a repetitive chirping noise coming from under the hood. It only happens when the vehicle is moving, usually under acceleration load. I'm thinking that it's just a bad belt that I need to isolate and replace, or maybe a tensioner pulley going bad - but it's annoying nevertheless. Not really a design flaw, probably just something wearing out.
4. The engine cooling/radiator fans - these things are on full-bore ALL THE TIME! Whenever you accelerate, all you hear are those damn fans - they drown out the engine completely, even with the windows down. While the V6 has plenty of power when we need it, it sure sounds like it's working awfully hard. I'm pretty sure that this is just another annoying Ford trait, but I'll call the dealership and ask them about it just to be safe.
Other than those few things, the Expo is roomy, comfortable for the most part, and has treated us very well. No major issues as of yet. It has about 65K miles on it now, so I'd like to think that if anything drastic was going to go wrong, it would have happened by now.
I'm looking at selling my Envoy and getting an Expedition to compliment the Explorer...but my GTP isn't going anywhere :)