By all means its awesome! :D Apart from a massive number of scenarios, there are 9 campaigns: 4 in Dark Prophecy, and 5 in the sequel Rise of the Elves. You just have to make sure that if you start a new human/demon/dwarf/undead campaign, you start with the Dark Prophecy campaigns. The 4 human/demon/dwarf/undead campaigns of Rise of the Elves are meant for your high level characters you created in the Dark Prophecy campaigns.

edit : ok, I just looked it up again, and it is more complicated than I remember. There is only one campaign in Rise of the Elves, namely the elf campaign. The other 4 there that I mentioned that are for high level chars, are shorter and difficult campaigns from Guardians of The Light and Servants of The Dark, which are bundled together in Gallean's return.

Since the OP liked Populous 3 I would second Sacrifice. It certainly is not a game for everyone, but I may hit the sweet spot in this case.

As for TBS: Heroes of Might and Magic 2 + 3 + Chronicles. Should keep one busy for months (if not years). Age of Wonder Series may also worth taking a look.

Try Age of Wonders: Shadow Magic or the Heroes of Might and Magic series. The battle system is similar