are we talking about existing games as isometric RPGs as the first post implies?
1. Deus Ex (can't stand how that game looks and plays, but would love to play a turn-based isometric version of it)
2. Wasteland (really liked it back in the day, but as more time passes it gets less and less enjoyable; the original is a less focused game IMHO, which prevented me from finishing it several times, a more polished Wasteland on, say, Tyranny's engine would've been a dream to play.
3. Fallout 3 (FO3 gave us New Vegas, but I wonder to this day, what if Black Isle or Obsidian actually had gotten to make it instead)
if we're talking about hypothetical games, though I'd go with:
1. Darklands 2
2. Jagged Alliance 3
3. Syndicate something-something
4. Ghost in the Shell RPG
5. Aliens RPG