This is something that interests me too. I agree with the whole soul thingy (possible cause of budget/publisher reasons), but I think its not only that. For me personally the golden age of pc games was around the time when games such as Fallout 2, Starcraft, UT, Deus Ex were released (with also a few years before it and a few years after it). I think one of these reasons it that at that time creating assets was less work cause the 2d sprites or 3d models were low res etc so more time could be spend on other things such as mapping and programming (my guess at least). I think this allowed teams of ~10 people to create AAA-sized games (which now require way more people and a result must cater to a bigger audience).

There were also less or no asset stores and templates so probably more had to be created in-house, which might also have led to more distinctive looking games.

Whatever the case, its not only nostalgia. Since sometimes I find & play an old game that I never had played before and which is fairly different from the games that I played at that time (e.g. Seven Kingdoms 2).

, does Age of Wonders 3 + expansions count? Also while I haven't tried it yet, perhaps Spellforce 3 (for a niche group I think).