How does the game lack depth. It's far deeper than a lot of mainstream games. Sure it's been streamlined, as most games are these days, it's just what earns money. However I've spent hundereds of hours in Skyrim and will very likely spend hundereds more.
I could go on indefinitely but I'll cut it down to a few points:
1. Awful, infantile writing with little to no character development: For our example we will take Farkas, a fairly important NPC. What do we know about Farkas? Practically nothing except that he's the dumb one, as he and everyone else love to bring up. The vast majority of NPCs only have one characteristic, which will be all they drone on about at you.
Bad dialogue in general is everywhere, e.g, in the opening segment, Hadvar/Ralof will run straight up to a wall, despite there being an obvious, lit path rift in front of them, and will say "This doesnt go anywhere". No [censored], Sherlock.
The Journal is but a fragment of it's past. The quest lines are short and often full of plotholes. Most quests are very unimaginative, and those are the ones that are luck to not be fetch quests. I could go on.
2: Removal of many more spell effects and skills: Burden, feather, a variety of summons. All gone for no good reason. Acrobatics and Athletics were removed because Bethesda couldn't be bothered to make them good (what about falling attacks, climbing, vaulting, flips, rolls etc.?). Hand to hand was removed wen it could have been folded into one-handed with fist weapons but Beth couldn't be bothered. And so on.
3: No degredation, no throwing weapons, spears, interesting different Melee weapons, crossbows until Dawnguard, battlestaffs, Halberds, wakizashis etc. Complete lack of difference between equipment.
You get the picture.