I would say "No", you get access to only about 4-5 (correct if I am(probably) wrong), and you won't even get 80% of your classes abilities. Hell, half the fun of the game is it's end-game, which can be anywhere between keyboard smashingly difficulty to you could be dead and still beat the encounter, based on who/how competent the other 9-24 people are.
I will say this: Yes, try it out if you have friends who play. That's what makes the game fun, I got into a semi-decent guild. They ended up clearing ICC, but only after it got nerfed 30%, but they were fun to play with when we got the right people together. Than the other guild I was in was just too good. We 10-maned 25 man ICC successfully, before the final few nerfs
If you don't have friends who play, Than I would say pass. About 75%(most likely more) of the game is still "Locked" to you. I mean, you can go everywhere (exceptions being the expansion only areas, and almost every dungeon), but you won't last long when you start encountering level 25+ enemies