I've highly enjoyed Skyrim. Sandbox rpg games for me are about how I personally develop my character. How I decide to do quests, not dialouge options or rewards, is my development. Level only matters for me in what I choose for my character to do next.
The real bread and butter for me is all the little unexpected things that happen from game design complexity.
Like doing the Dark Brotherhood quests, understanding the lore of the destroyed Brotherhood and what I wanted to become of the Brotherhood. I walked outside and Lydia (companion) was standing next to a slain dragon, by all appearances she killed it. I went to examine, absorbed its soul and I hear 'Still here!' from Lydia. I later married her.
Then, once, I had a Dragon appear randomly as I was looting some Bandits in The Reach. It was mayhem and chaos.
I can't recount how many times I've been caught between skirmishes of 4 Stormcloaks and 4 Imperials while doing adventuring on the front lines, or seen prisoners rescued by Stormcloaks or Imperials on the front lines.
Or fast-travelling to Riverwood. I had a high bounty on my head on a different hold, and a gang of Bandits showed up to take me. But at the same time, a dragon attacked the village. The very same moment, a thief ran past through the village out into the wilderness.
There was a proper battle with all the chaos going on!
And being a theif or an assassin, getting caught in the act and the escape necessary to get out of dodge. I once jumped my horse off a bridge in The Reach into a river to get away from town guards. They shot at me from the bridge while I swum down river. As I got further down river, some more guards assaulted me, and I faced bandits while leaving the hold.
Not to mention all the little moments of watching packs of wolves chase down Elk and Deer as they flee for their lives, hunters in the deep wilderness stalking prey, and by armok the vampires! I helped a whole family of some and didn't even realise, and I'm afraid of little children now!
Or how about dragons attacking in the middle of cities, or hell I had a dragon get mixed into a battle over a fort! I mean, I savour games like Skyrim, Oblivion, Fallout and even Dwarf Fortress for their little odds and ends that all add together to make something incredibly unique and absolutely never the same, even if you're doing the same quests over and over. And with different paths your character can take, different classes and different decisions.. I mean, I can be a sneaky guy with a bow, or a sword, or even a lowly dagger! I can be that mage who can either raise an army of the undead or summon powerful monsters! I can be a berserker with two axes and heavy/light armour, a knight-based character, a theif, an assassin (without even needing the Dark Brotherhood), a treasure hunter or flippin Indiana Jones, and have the entire world develop in amusing, enthralling or interesting ways.
But thats just my 2 septims.