Morrowind was for me, the most replayable, and hands down best RPG created to thiss point. I think I've dumped solid months into the game + expansions + Modded stuffs.
It's getting on in age now, so the graphics aren't as stunning, and the NPCs aren't as engaging, as some of the newer titles, but it is still very enveloping as long as you follow in some way, one of the main quest lines, be it a faction questline, the expansion questlines, or the Main questline. If you just go a-wandering, your bound to get bored at some point.
The combat style is kinda dubious, but I usually use a bow or magic, so it doesn't often get to that point. But I also like the story, above and beyond the combat system. It's really engaging to me. And some of the enviroments are pretty scary, the first time you enter a crypt, or the Red Mountain, your bound to get a racing heart. Even dwemer ruins will raise your blood pressure.
I think you'd like it. It's fun and engaging. PLus Game Of The Year version isn't even expensive anymore for several hundred hours worth of gameplay.