I first played oblivion and enjoyed it, albeit the combat felt shallow. I recently reinstalled Oblivion with well over a dozen mods on my new PC, after several years, and am pretty impressed.
I played a bit of Arena a decade or so ago. I think this series has had some general design flaws that have changed as it moved into 3D.
Morrowind is really natural and dangerous, but the RNG combat is not great.
I think Skyrim fixed a lot of the series problems in creative ways and deserved the attention it received.