These games are old and crusty but still my very favourite 4X's ever! IV and V have been widely available but I was worried that the OG versions were lost forever. I highly recommend III, even though it is very primitive. The way that combat & weapon targeting works in III is unique (as far as I've seen) and the simplistic 2D graphics are delightfully easy to mod - even for a completely unskilled nub like myself.
Amusingly terrible and surprisingly twisted and kinky. Not a game for kids - not really a game for anyone when I think about it - but it is worth a play through if you are feeling nostalgic for full motion video and ridiculously illogical puzzles (thank heaven for online walkthroughs). The only reason I can't rate it higher is the final act. It goes completely bizarre at the end and really tests your dedication as the game descends from cheesy and awful into "oh my god why I am wasting my time with this".