In terms of previous games Skyrim has potential to surpass them all.The only one it pretty much hasn't surpassed yet is daggerfall, and then we have to discuss what exactly we mean by depth. Depth in what area.
Sure Skyrim has the potential to surpass them all, but I sort of doubt we'll see that realized. Oblivion had that potential too, so will the next one. Depth I think, should be found in all areas of a game. If the game has a really great combat animations, and really solid controls and a complex control layout that allows you to parry, block, dodge, disarm, trip, suplex ect. ect. ect. but has a storyline that railroads you into a single course of action with no options for role playing can you call that a deep RPG?
I would say depth requires a number of things. Quality and quantity of content, quality of storytelling, game mechanics that are coherent, fun and detailed enough to create a rewarding learning curve.
My impression, and what seems to be the case in most of the games I grew up loving (see Tribes and TES franchises) "accessible" seems to imply dumbing down the gameplay to essentially remove the learning curve and grant instant gratification for the lowest common denominator.
Hopefully I will be surprised by Skyrim, but every time they mention "removing skills to eliminate redundancies" or something of that nature, my hope is diminished. I for one want redundancies, multiple ways to approach the same problem and skills that aren't necessarily going to help me slay monsters, but could be fun to play around with. Furthermore, I don't want practice with a dagger to magically make me highly skilled with a longsword.
For me, the most appealing part of TES has always been the openness and the options (with consequences). It seems that every new game since daggerfall has been getting prettier and taking options (and consequences of your choices) away.
(Edit: Having read your latest post, you may have restored a bit of my hope about consequences.)
That said, I'm sure it will be a fun game that I will put a lot of time into. Bethesda has yet to make a TES game that I didn't enjoy on it's own merit. The problem I have is the trend toward simplification and mainstream appeasemant that has transformed a detailed rpg into something more akin to an action/adventure game.