Generally the exploration part is really boring on an alt. In other MMO's yeah, you do the same stuff, but it's mostly just fighting mobs and that's roughly just as interesting regardless of the character you're on. But redoing the more tedious hearts and traveling to locations you already know just to get a vista or a PoI is boring.
But much depends on the zone really. All I'm making is human characters, gotten about 10 of them up to level 12+ and I still love Queensdale even tho I've done much of it on all the characters. On the other hand nothing about Metrica Province clicked with me even the first time i've done it. And the thought of returning there to 100% it on an alt makes it feel like a chore.
See, my main is an asura, and I quite enjoyed metrica province, but I've tried to make a sylvari alt, and I just really dislike their starting area(which I did on my asura as well). The underwater sections really annoy me for some reason. I probably should've made it a norn or charr, but the norn starting area never clicked with me in the BWEs. I'm currently just trying to hold out until I can branch out of the areas I've explored, and maybe head over to the other side of the map and do some of ascalon or something I haven't explored a lot of.
Unfortunately the alt is the result of me no longer enjoying the engineer class at 60. I'm not sure what happened but I was feeling very weak on my engi and really not doing as much damage as I felt I should've been. Playing my ranger I can easily solo most things, and I do decent amounts of damage in WvW, but dual pistol engi did not seem to be cutting it in WvW. Not enough damage (even though I'd stacked precision and power), and I'd melt almost instantly if I didn't stay at the back of fights. Probably just need to take a break from him and come back with a fresh mind about how to build him. Rangers on the other hand, that short bow is ridiculous for 1v1 and the long bow is great for sieges. So far been doing alright in WvW, and pretty good in PvE as well.