I like levelling for most of the reasons people have already given for liking it, and agree with most of the reasons for it being worth doing anyway.

My reason not to like it is gone now. It was because I kept getting stuck, unable to level. For that reason, my first high level character was little more than a tank, since I didn't know support classes very well, and I figured I could keep a quick pace by being desirable to groups. Now, there's no more 100,000xp holes from a few unlucky mob deaths. Back then, once you were 30K in the hole, it wasn't easy to get out without another mob death, unless you were extremely patient and only advanced by killing mobs with a very low chance of hurting you. (getting 100xp per kill if you're lucky)

While I'd like more experience from other things, like automated quests, RP, and exploring, by no means should those things replace the usual ranking method, just help it along. A lot of RP is based in going places, meeting people, getting beaten to a pulp, beating others to a pulp, and so on. We'd lose too much of that if people didn't go out to kill mobs, because we'd lose so much risk factor.

As for exploring areas, apparently I can't keep my mouth shut, so my previous comments just aren't there now. The only real advice I should have given about them is this: Don't go to far off places for easy experience, it's not worth the trouble. Go to far off places to learn about them, learn what's there not just in gear and mobs, but also for strategic means. If you want to catch people in places that for whatever reason helps you win the fight, that's great, but it's also good to find places to hide and/or make a stand for when those hordes of people come hunting you.