Homeworld was the first of it's kind, I had no clue what I was in for when I first bought it, I remember thinking the firt scene in the game was a loading screen until I realised I could rotate it, it utterly blew my mind, something a game hasn't done for a long time.
Homeworld C was a nice game, with a lot more variation to it than the original, but it suffered from slightly more 'cartoony' graphics, and a weaker plot.
Homeworld 2 was awesome looking, but was actually a step backwards in my opinion. Homeworld, whilst an incredible game, was often slated for a lack of variety between the two main races. Homeworld 2 has some variety, but the roles and performance for various ship types are the same, fighters, corvettes etc. It would have been nice to have one race which has incredibly powerful corvettes and fighters, but their capital ships are weak etc. Originally, HW2 was going to have 8 unique races available for multiplay, including Bentusi. I wish Relic had stayed with that plan and not rushed the release .
Homeworld is an awesome game, Homeworld 2 is great, but relies too heavily on the word 'Homeworld' and not enough on the number '2'.