I would say that the only other 'isometric' RPG that I have ever loved with the same intensity (indeed, at times even more so..) as the original Fallout games are Baldur's Gate and the related sequel and expansions. The Icewind Dale series is of course extremely similar with the exception of the edition change, but they lack the replay value in terms of meaningful choices in dialogue, not to mention the class-specific strongholds introduced in Baldur's Gate 2, and the lack of NPCs with fleshed out personalities across the alignment spectrum. They are also 'apparently' more linear; while Baldur's Gate and Baldur's Gate 2 are both linear, they present more locations spread out across the world map that can be visited in many different orders and give at least the illusion of being open world, whereas Icewind Dale has an extremely set path that must be followed. Both series are masterpieces, but I replay one far oftener than the other, for the reasons I mentioned. There are still two strongholds I've never seen, romances I've never completed, builds I've never tried, dialogue options that 20 years later I am still surprised to uncover, &c.
Close contenders would be as mentioned Arcanum, and Temple of Elemental Evil. Planescape Torment exists in a realm of its own where it plays more like reading a bunch of interconnected novellas or short stories, and is admittedly on par with Fallout and Baldur's Gate though I have to take longer breaks between play throughs for this very reason (although with the amount of choices available, this does not become noticeable until you've gone through it at least two - three times). I thought Wasteland 2 was enjoyable and well made but I'm not a fan of the moveable camera and pseudo-3d polygonal objects and NPCs, I get a jarring disconnect when I see a fully animated 3d model motioning at me while a stark, emotionless dialogue box represents their interacting with me, and for this reason I've not made it very far into most of the isometric renaissance games to release in the past few years (Pillars of Eternity, Divinity, the Pathfinder: Kingmaker campaign), I have a much better acclimation to this in the style of presentation found in the older games in which much more was left to the imagination, as in tabletop RPG gaming. The hand painted pre-rendered 2d backgrounds of Baldur's Gate are to this day the best I've ever seen, and nothing quite offers the same experience. Also the way the world map in Fallout and Fallout 2 are handled, is absolutely perfect.
My girlfriend bought and played through all of the Shadowrun games that came out over the past decade, but I have yet to try them. I loved the original that I played on Super Nintendo as a kid but once Fallout was released it blew anything I'd ever seen previously away.