I never really got into Oblivion due to the way levelling and level scaling were handled, and some of the aesthetics (glass weapons; armour; everyone's faces, Orcs in particular). I would've liked Morrowind if I played it at the time, but now it's a bit too clunky and bad looking for what I'm used to; I always think a handheld console port of these old open-world games would be cool though. As for Arena and Daggerfall... I don't even know. Daggerfall seems kinda cool with all the skills it has and the huge map, but again with the dated graphics (and sound, in this case).
Skyrim is where my interest really took hold, despite my lament over removal of the old stats system (strength, intelligence, etc.) and spellmaking. Those were great things to abuse (see Veriax's abuse of Sujamma early in his Morrowind LP). My main thought prior to release was how much better the beast races and Orcs now look. After first playing, the one idea I warmed up to most was how Smithing upgrades can make iron and steel equipment entirely viable throughout the game. Looking all fantastic in brightly-coloured magical armour never sat well with me. Along with our shared opinions on what ores are worthy of digging up, I like the overall characterisation of the Nord people. Could be a lot better, but also a lot worse knowing Bethesda.
I find the combat system of Skyrim to be remeniscent of Dark Messiah's. Not quite as fluid and I miss that lovely disarming animation DM has, but I really enjoyed that game and wanted its combat to be in a something like TES... and then it pretty much happened! It would be nicer if humanoid enemies used their shields more effectively, but there are probably many AI mods that would rectify this. Stealth is a lot better than Oblivion's too, although the intelligence of NPCs in this regard is left wanting. Destruction magic is meh; without the ability to make one's own spells, one just can't get much damage out of it since there's no material upgrade path.
Mods, then. Nothing that majorly changes the game. I use the unofficial patches, SkyUI, A Matter of Time, and a blood texture mod to replace the blurry on-screen effect.
Well, that's enough from me. Hopefully being one day late to reply doesn't get this thread locked.
The only negative comment I really have towards Skyrim, other than Dawnguard, is the fact that once you get your armor upgraded/enchanted, it's impossible to die on Master difficulty. And by impossible to die, I mean replace their arrows with toothpicks and experience equivalent damage.
Make your armour skill legendary when it reaches 100 and you'll die in 2–4 hits... actually probably 1, unless your character is like the one of mine I did that on with about 500HP buffed to over 700 by enchantments.