As for me..
Arena - It had a decent story, if you ask me, and a very interesting boss. But lacks choices and has a lot of annoying restrictions.
Daggerfall - Prolly the best of the best, for me. Love how big the dungeons and landscape are, even though they were randomly generated. Love all the choices and the fact that you can do whatever you wish, and such.. Though, glitchy at times, but still so good and fun to play.
Morrowind - Very good, very well made.. Though I do not like the combat at all as well as the luck system. Annoyed the heck outta me. Didn't like the Argonians in this one either.
Oblivion - It was okay. Had some awesome NPCs in it, like Lucien and Martin... It also had some of the funniest quotes I've heard in TES series... But does lack a lot of weapons and other good stuff..
Skyrim - Good. Could've done the quests better but they were decent, and some were very interesting. Glad they brought back the Random Generated Quests. It has a lot of other stuff that I like and also has some of the most breathe taking sites that I had ever laid eyes upon in a game.. Also, is slowly becoming my favorite game.. Maybe in a few more DLCs, it will be if Bethesda does it correctly.