I've never played Med:TW1 I only really got into it from RTW onwards. I wouldn't be put off further games from a game in the series, as said previous the game is always being tweaked. I mean, I bought the Command and Conquer 'a decade on' series and playing C&C1 again shows so much things which were missing that was added later.
Med Total War 2 will kick ass. if you computer can hold it, buy it