The fifth or so installment in the Grand Theft Auto series is the best, with very few exceptions. Rockstar did an excellent job building upon the strengths of GTA3 and Vice City to create an almost overwhelming experience. San Andreas is approximately six times the size of Vice City, which means that there is always something to do or somewhere to go. But right away you realize that all this space can make it a real pain later in the game when you have to commute in between cities. Sometimes it can take 10+ minutes which makes the game very tedious.
Most of the missions are pretty exciting and serve a real purpose. I feel, however, that many of the missions do not really provide a huge challenge. Even missions on Las Venturas, the last part of the island you open up, some of the missions are simply "take item or person X to location Y." Perhaps they mix it up with you having to kill some person, but that is mainly it.
Like Vice City, this game leads you into a world that essentially has forgotten you, and you work your way to the top. It is still a great game overall and it has sucked up several days worth of play time. 100% completion could require as much as 100 hours of gameplay or maybe more.
9 out of 10