3 has a really nice feel when you manage to get the early timing attacks off against the neighbours, but the later half of the game is too solved - the game ends with infantry + artillery stacks being the only units you need, and with the 3x4 city grid bring optimal.

4 in contrast had a bunch of different paths to power, and those worked even on high difficulties. There were also no optimal city grid the same way (though still being denser than civ5).

3 is still my favourite of the series. 5 was good too, but 3 overall feels complete and had great graphics.