Arcanum replay value

I'd say absolutely. Play it as a magic user, then play it as a technologist. You can also do elf/dwarf/human but in those cases the differences are more cosmetic. It's also fun to try out different specializations: the masters for the highest levels all have different quests.

There are also tons of side quests. It's unlikely that you saw them all in a single playthrough. Different party members? Lots of stuff.

I'd say you could play this game at least 3 or 4 times. Even if you stick with science, you never have enough points to max out more than a couple of the disciplines. Try it once with chemistry and medicine, and then again with firearms and explosives. Same for magic.

What I find really changes the nature of how you play the game is whether you have skills that allow you to attack from a distance, like firearms and explosives, or skills that work better face to face. This will affect your role in the party and you support the other characters. World of Warcraft simplifies this a bit with the Tank/Damage/Healer setup, but in arcanum it's a little more fuzzy. People can still take on these roles, but its not officially designated.

Personally I just like making grenades and hucking them at people :)