Honestly, I don't really care how long, time-wise, it takes to reach max level. Because of the unique class storylines and the encouragement to play alts, if it doesn't take long to reach 50 on one character, I think that's perfectly fine.
However, what does bother me, as many others have stated, is the fact that it's so easy to outlevel the content. I started out doing all of the missions with bonuses, as well as the space missions and flashpoints (once each, only). Once I realized I was outleveling content, I stopped doing the bonuses. Even then, the pace in comparison to the content wasn't slowing down, so I started stealthing my way through everything I could and only fighting if I had to. Still, I'm outleveling content (currently 31 on Alderan in the 28ish area).
Don't misunderstand, I think the amount of content is absolutely superb. And the fact that I'm actually interested in all of the missions due to the story is a huge plus. The biggest problem, in my opinion, is what seems to be an imbalance in xp gain (as has been stated by many others in this thread). It just seems odd to me that the game would be designed for one to be level-appropriate only if they skipped the majority of side-quests.
I like the two suggestions I've seen so far - drastically lower the xp gain from green quests so that the content can "catch up" to you, or have an xp off feature. I also wouldn't mind seeing the xp in space missions cut in half, but that's not a huge deal - if you do something "extra" like that, I guess I can see it throwing off your leveling curve (though I wish it weren't quite so drastic).
On a side note, I'm seeing a lot of posts in the opposition that seem to be taking things to the extreme. From what I've read, most of the people who are discussing the leveling issue are not complaining lack of grinding or too much content, so I'm not really sure why people keep bringing that up with snide "you'll always find something to complain about" comments. I believe this is a valid issue - the content is wonderful, so why should a player be forced to skip through many parts of it and miss experiencing it just to stay level-appropriate?