"Eador. Genesis". Perfect for a long, thoughtful single-player experience. I like it more than the third and fifth installments, but it requires more thinking and has a higher barrier to entry.
PS: "Developer's Workbench" evoked nostalgic feelings for the year 2000, with a P-II 450/96Mb RAM/6Gb HDD/ and Win98SE (later Win2000 SP4).