Keep asking myself the same whenever I see discussions about replaying, and replayability, why would I want that. But interesting that you mention Arcanum, since that's a game that I did restart several times (and never finished as a result). But there it wasn't character build (one I restarted once due to poor choices was Icewind Dale 2, but wasn't far along, realized I had a really crappy party, mitigated damage to restart then), it was the fact that I was playing without reading a guide to see where companions were and due to them having set levels when joining and only advancing when the main char does, I wanted to get them at the right level (or one below, as they wouldn't join if you were more than 1 below) and keep all at same level, so was exploring and rushing to areas to find them first. And then there were also some bugs that I only noticed too late to go back, like I remember a cursed weapon that dropped a stat that wouldn't restore when unequipped, and equip it again and it'll drop even further, and I only noticed after overwriting even earlier saves. That was awfully frustrating.
Other than that, just replayed some (that had a beginning and an end, I mean) back when I was little and didn't have access to many games. Quest for Glory 2 stands out, played that lots of times, but probably "only" finished it a few of those times. Even in games where the conclusion is just winning, like Civilization games (or Alpha Centauri), or Tycoon games, I tend to just win once and move on. Played 2 games of Civ4 to victory and that was an exception, but because first was on a computer that could barely handle it, was barely crawling, and then had a proper game on a better computer. Another exception is Colonization, played and won plenty of times, but again from back in that day when I didn't have access to that many. And then there was Transport Tycoon Deluxe, but there were multiple scenarios and I just remember getting to 2050 once in all the times I played it (and when I had just left it running, and saw that newspaper on screen as I passed by my room, assumed it'll pause, went to eat, came back, it was far past that point, hadn't paused... I never got there again to see what that newspaper said).

Mainly play to see a story and some characters through to the conclusion, even if in some games that may mean winning, more clearly if it's winning a series of scenarios, but even if it's just one big game, there's still a progression, an atmosphere, some sort of narrative you can see in it. (I much prefer those with actual stories to play through and immerse yourself in, escapism of that sort, otherwise the gameplay needs to be truly outstanding, and even then, like I said, need some atmosphere, some at least implied narrative...) Once I get there, it's done, close the book on it, move on.

Let my throw "FreedroidRPG" in the discussion. A nice little freeware RPG, inspired by Paradroid.

Might and Magic X is a great old school blobber that pretty much no one bought or talks about for whatever reason. Maybe because it's Uplay exclusive (I think?) or something. I high recommend it though if you like those types of games.