Skyrim's Dungeons are better designed then Oblivion's but there are other issues at play and a few repeated mistakes.
I'd say the old issues still around are
- the overuse of certain prefabs and meshes... why do almost all inns look near identical across all of skyrim? why are there so many circular wooden stair cases in ancient nord burial chambers?
- a lack of variation in artistic design of dungeons of the same type. Apparently all dwemer like their goldish colored metal and cement tunnels, they also all hired the same architect to build their lairs with all the same doors.
- Numerous battles against the same mob type... Draugr dungeons feel even more repetitive and bland then goblin only dungeons in oblivion.
New Issues I would say are
- Mob Layouts, Oblivion mob layouts were pretty decent, but in Skyrim they seem pretty lame. I can't put my finger on the cause of that but the change in combat plays a part in it.
- Dungeons are less enjoyable, they might look pretty but more happened in oblivion's dungeons then in skyrim's.*
- How many times do we need to do the same claw puzzle! I think I've come across, what 8 or 9 claws, one claw is even used twice in the same quest!
* For example in one dungeon in Oblivion (I believe in the Thieves guild Quest line) You have these two massive blocks which turn out to be walls containing a number of undead. Sure there are rooms in Skyrim where Draugr jump out of their coffins, this however happens a lot. While the design of each dungeon in skyrim is unique, the tricks, traps, puzzles and scripted events are not, this takes away from the dungeons A LOT.