Old, but well, GOLD. ‘GTA United’ was a ‘total-conversion-mod’ for GTA San Andreas, which lacked in missions, but for free-roamers, It’s fun.
All features are the same as SA, but the thing, that makes it special is it’s map, comprising only of, the whole of Liberty City(from GTA 3), and Vice City. The two cities are only inter-accessible by sea, or air; no land route.
The fun-part is that it kinda enhances GTA3 and Vice City, so the lack of missions doesnt account for much. All the Clubs, in both the cities are slightly real-er as they are in SA. Same goes for the Clothing and ammunition stores. You no longer get one outfit per store, but can shop for whatever ones you like, but when it comes to the Ammunition stores(Ammu-Nation), I sometimes miss the vice-city ones; much faster, though i agree that they were not at all real, seeing as the dealer hardly ever moved.
Apart from that, you can swim, which would come in handy while performing crazy stunts, while on the run from the law.