Vice City is very cool to play Flops, although too has some very tricky missions.
It does however have a fantastic feeling of nostalgia about it, with very entertaining radio stations playing great tunes, and really great characters to play with. And through the mods found all over the net, you can add almost any car you like into the game. You can get it for a few quid now second hand so well wortth a try (check out ebay or local 2nd user shop).
GTA2 wasnt as good, imo, as the first one although did try to add new features to the game.
Then GTA3 was the first of the 1st person GTA's, opening up a whole new area of gameplay for GTA fans. I liked it, although yes it did get very tricky. I got 100% complete once then never played it again.
GTA:Vice City - the best I've played so far. Completed loads of times, and still play it now. Found it v addictive.
GTA: San Andreas - awaiting PC release (June 10th I believe), and not played console version yet.