the game is still enjoyable, for me at least, due to the amount of content now there at the end. and i guess the levelling isn't such a
bad thing, just different to what it used to be. i guess some servers, especially the 'normal' servers may be better for levelling groups than others, and it may be better in a levelling guild even. i tend to have my alts in my own guild though, as i'm the guild leader, so i like to know what's going on even if i'm on an alt.
best thing i could suggest, if you're looking at going back to join some friends, ask someone to set you up with a Scroll of Resurection. it lets someone reactivate your account for a few days for you, so you can try things out. if you resubscribe, the referer gets a free month out of it too, so if it's a friend, get them to share the savings

other option if you're looking at a fresh start, would be to get a trial account first, just to ask around on different servers and see how things play out in different realms and such.
All of the experiences i have are just from the horde side on the Burning Steppes server, so it may not be the case on other servers, or even for another player in different situations on the same server.