I got into the whole elder scrolls thing pretty late, with Oblivion. When I first played it on the PC it seemed pretty great- the grahpics were good, the world was interesting and open, and the ability to mod it was new to me as well, and very awesome!
Fast forward three years to my second playthrough. Even with DLC, the main storyline seems incredibly short/uninteresting, where you're pretty much just a bodyguard for the world's most boring bastard child of Jean Luc Picard Sir Patrick Stewart Uriel Septim. The majority of the game seems contained within side quests, and every 10 or so minutes you come across another oblivion gate that wants you to walk into a generic environment and close it.
At first I at least thought the levelling system was unique- until I realized that they've been doing a close variant of it that debuted in Japan under the title of "Final Fantasy 2". Combat is incredibly mundane for an rpg, as it usually includes a variant of "hit them with a weapon or spell more times than they hit you.", and that open world that I loved... you never really affect or change it. It all just feels so static when compared to other rpgs or games in similar settings.
But my biggest, most hated complaint? The voice acting. I think it's great that they took time to put a voice to every part of the script, but if you're going to do that, at least make sure that two people that sound exactly the same despite being different races are never standing right next to eachother. It just seems like they blew the entire voice budget on Sir Patrick Stewart and then picked 5 people off the street to finish the rest of it.
Ugh. Despite all that, I'm really looking forward to Skyrim, and when it comes down to it, I'm very hopeful that it ages better than oblivion does.