(OK, so I haven't done the Empire questline, but that's because the start of the game found me with my head on the chopping block by the hands of the Imperials -- why would I help them after that!?)
I've spent 180 hours on the game. It's big, though the main questline itself isn't that big. But there's a lot to do. (Yes, there is an infinite number of quests, but those quests are of the type "go there, kill this, get back" -- you have to be pretty dull to find that interesting for very long.)
I've played a sneaky archer, a style that meshes well with me -- just like I played a sniper in Mass Effect. Some of the things are pretty stupid: you shoot people and creep away, then if they can't find you within half a minute they'll just return to their posts, assuming they imagined the arrow sticking out of their head. I've occasionally had to switch to melee weapons, but I've tried to avoid that. I like that skills do improve with use, but some skills are too easily spammed to be taken seriously -- for instance, I started smithing when I was level 35, and by the time I hit 45, my smithing was at 100. I must have made thousands of iron daggers, and they all counted towards the skill points. Same with enchanting and alchemy.
The game is very open-ended. There is no fixed order, which is a strength -- but also a weakness. If you accomplish something like kicking out the Imperials, some things are different when you return to that part of the province: like which jarl is in power. But all of the other things are exactly the same, and then it doesn't seem like you have a lot of influence in the world, even though you brought about a major change!
Another dissapointment is that you can't really build up a relationship with people -- something that I liked very much about Dragon Age. In Skyrim, you fetch someone's sword from a cave, and they love you. They'll follow you into dungeons, and may even agree to marry you! And then when you are married, they just hang out at one of your houses and merely wait for you to return home. I missed that.
I've had a lot of fun with Skyrim. My next game will be Xenoblade Chronicles, because it's time for a JRPG again!