In Oblivion, there 199 TOTAL quests (main and side) and there are 367 TOTAL locations on the map. This is excluding all dlc.
In Fallout 3, there are 31 TOTAL quests (main and side) and there are 161 TOTAL locations on the map. This is excluding all dlc.
In Skyrim, we have been told that the main quest will be "approx. 30 hours" and that there will be "more than 130 dungeons" and "over 100 points of interest". If we assume that the dungeons and points of interest are separate, we could conclude that there are potentially a minimum of 230 locations. This is HEAVILY speculatory as the dungeons and points of interest could be combined and average playthrough length is very much relative. If indeed dungeons and points of interest are combined, then that would mean we would potentially have a minimum of 130 dungeons/points of interest.
Also, according to recent interviews with Bethesda employees, we have heard that the amount of quests in Skyrim is "5x the quests that Fallout 3 had", which would mean that Skyrim would potentially have 150 TOTAL quests, 50 less than Oblivion.
I'm excited about Skyrim and I will pick it up regardless, but is anyone else concerned that there might be somewhat less or significantly less content than Oblivion?
Nope. People judge the game quantitatively and that's a fool's assessment. As I've said many times before: I've never seen a review take points off because there wasn't enough half-done missions. I have however, seen countless reviews take points away because what there was to do, was [censored].
It's seriously not that hard to ... realize that taking a game's content down a notch quite often means, especially with games this AAA, that the content that's in is being focused on way more than the previous, more numerous iteration.
Skyrim's philosophy is to reduce slightly the number, and significantly up the quality of that number. You also didn't even mention random events. There's no evidence that Bethesda has quantified them at all. Plenty of random things happen in the previews and they lead to missions. But when those missions are completed, there's nothing stopping them from continuing as Red Dead style random events that just don't lead to bigger things.
Entertainment's biggest axiom is how good it is. Now how MUCH of it there is.