I don't hate Skyrim, but my major gripes are (and these apply to Oblivion, too; I haven't played any other Elder Scrolls game):
1. Lack of compelling characters. Most characters you encounter in an Elder Scrolls game may as well be a Quest Board from DA:O. They'll have one of the same ~seven voices, no unique mannerisms or characteristics, shallow motivations, etc. If followers did not fall into this category then it might be forgivable, but TES games never feel alive because the characters that inhabit them have no souls.
2. Lack of compelling plots. The only decent plot in both games is Oblivion's Dark Brotherood plot. Everything else is very straight forward. The game does not inspire the player to invest any emotion in the game because the plots (and, again, the characters) are by-the-numbers fantasy. Some of the better "plots" in the game are just very small scenes you find on your own.
For instance, I found an abandoned mine with a journal which told the story of two friends who got a gold mine together. They unfortunately did not find any ore veins, and one day one of the friends simply disappeared. The author assumed it was because the mine venture failed. If you jump up to a branch of the mine that's not easily accessible and follow it for a bit, you come to a small room with a skeleton crushed by rocks and a gold vein.
It really doesn't help that they prop your character up to god-like proportions. There's no suspense or tension. At no point do I feel like my character isn't going to hack-and-slash his way to victory. This brings us to...
3. Almost insultingly grandiose. Most fantasy games have you become some major world figure. DA2 deconstructed this by having Hawke turn out to be just an ancillary character in the story of Anders, but that's a rarity today. TES games take things to a whole new height, however, having the player interact with gods, and kill god-like beings (with only 1,000 slashes of a regular sword, too!), and become the leader of every faction in the area by doing a handful of quests. It is fairly impossible to play a normal person in an Elder Scrolls game.
In Skyrim, for instance, if you want to join the Empire in the Civil War, you talk to the general who is leading the whole thing. Regardless of your rank (though you get promoted with each quest you do), right off the bat you're in the war council with the general and his most trusted advisers.
After doing two quests for the Companions, you're inducted into their exclusive inner council. After only one quest at the Mage's College, you're wrapped up in some ancient magical conflict that only you (and none of the other 20 college members) can solve. It's cheesy, but it's also stupidly predictable. I'm currently going through the Dark Brotherhood quest for the first time right now, and I would be shocked if I'm not leading this whole outfit by the end.
4. Lack of cinematic quality. In Mass Effect, when I talk to an NPC, the camera takes over (either when I initiate the conversation or even when I open a door or get close to said NPC). The camera follows my character's advancement, perhaps showing the reactions of other characters in the background. Eventually I reach my destination and I choose to say something to this NPC. Perhaps my character is chastising this NPC for something, so he points his fingers accusingly. Perhaps my character is threatening this NPC, so he draws his weapon, and the NPC cowers. My character can push people out of windows or punch them in the face. If my character is speaking to a room, he'll look around as if giving a speech, and make gestures to the audience.
In Skyrim, I run up to an NPC, and the camera zooms in slightly, but remains fixed. My character and the NPC remain motionless for the entirety of the conversation.
5. Bugs and poor planning. I actually don't care too much about bugs, especially because the community can fix most of them. What annoys me most are things like The Dark Brotherhood having you kill quest givers, making those quests unable to be started. Why? The Dark Brotherhood radiant quests can even lock you out of getting an entire Hearthfire home. There's a radiant quest to find various books all over the map, but if you find one of them before you get the quest, then you can't complete it. This is a casualty of the sandbox, of throwing a ton of rubber balls into a box and hoping none of them collide as they bounce around randomly.
6. Poor gameplay, lack of balance. I'm currently (trying) to play a Bow/Sneak character right now. Any given dungeon typically involves me one or two shotting bandits as I make my way through it, which is fine. But every once in a while my arrow-to-the-face will only bring down a random bandit's health by 1/20th. Then I either have to switch to one-handed weapons (and likely get two shot) or kite for ten minutes, pumping dozens of arrows into what should just be a mortal person. If I turn the difficulty down, then I one shot that same enemy and my sneezes kill the rest.
On the other hand, if I use Blacksmithing and Enchanting, even without abusing Alchemy, my character becomes unstoppable. I one-shot dragons and my health barely drops when I'm hit by a giant. If I turn the difficulty up, then we're back to square one, what with the dozens of arrows nonsense.
Dragon Age: Origins could be trivialized with Blood Wound and some other spells, but for the most part it was at least consistent on any difficulty. Mass Effect 2 on Nightmare is probably the most balanced RPG in recent memory. Even when playing a Mattock Soldier, it still took the right team build and strategy to do well.
All of that said, I'm going to go play Skyrim right now. I've just yet to make it to even level 50 on any character, and I don't see it happening this time, either.