I don't feel I am an expert by any means, though I have played WoW since Beta, a little EQ and FFXI before that and at least beta tested if not bought and played most MMORPG releases since then. Typically, I am a raider though I enjoy some PvP on the side. I somehow missed Rift at release. I had heard about it, but never really tried it. At one point I tried a free trial week or weekend, and I thought it was pretty good, but I was content with WoW at the time. Later, after getting bored with SWTOR's end-game, some people I played SWTOR with convinced me to give Rift a real shot. Seeing as there wasn't going to be anything new in WoW for a while, I tried it out.
Been playing for almost 4 months now and no way I am looking back. The interaction from the devs is great, you see GMs come and talk in an open format in global chat channels. You see new content coming out, I came in at 1.7 and there have been 2 major patches since then, in the little over 3 months I've been playing. Several leveling paths so you don't get bored as easily, and all are completely viable, and they added the low level IA since then.
Plenty to do at end-game, almost impossible to get bored. You can PvP, and with the recent addition of Conquest you can "catch-up" easily, you can go to Ember Isle and do the Onslaughts and Dailies there, you can do World Events, you can run dungeons, I am sure there is more. If anything, there is so much it is practically over-whelming. I am still struggling to catch up PvE and PvP wise, partially due to my limited play time, partially because there is just so much to do.
Also, the game is growing at a pretty steady pace it seems. Perhaps it is due to the revealing of the Xpac, perhaps because WoW is in it's lull before the Xpac, perhaps people are leaving SWTOR and looking for somewhere to go. I don't know the reason, I just know I am seeing tons of new and returning players. 1-29 chat is full of people asking newbish questions.
There is no other game I would rather give my sub money to, and the game itself only costs $5 from the website, though no free time with that. Still, that's $20 to get in for one month, that's better than any other MMO I can think of.