Hi, this is a long list that i typed, so please read it. Thanks.
GTA: 4 - No gyms to workout in
GTA: San Andreas - Gyms to workout in
GTA: 4 - Limited selection of clothing
GTA: San andreas - Extensive selection of clothing
GTA: 4 - New and realistic shooting system
GTA: San Andreas - Old, bad and unrealistic shooting system
GTA: 4 - Improved graphics and shading
GTA: San Andreas - Basic 3D graphics much like previous titles and little shadows.
GTA: 4 - No weapons or miscellaneous skills.
GTA: San Andreas - Miscellaneous and weapons skills.
GTA: 4 - Only helicopters available for flying.
GTA: San Andreas - A wide variety of planes, helicopters and jets.
GTA: 4 - Never before seen features like the internet and cell phones (you can call up friends, recieve texts and use the camera for photos)
GTA: San Andreas - Doesn't have the internet or wide-spread use of mobile phones.
GTA: 4 - 200 flying rats must be killed. More interesting side missions -asassination tasks, car exports for Brucie, vehicle thefts for Stevie, along with street, boating and helicopter races. Sometimes random individuals can be found who will assign you a set task.
GTA: San Andreas - Requires you to find 50 oysters, spray 100 gang tags, take 100 photographs and collect 100 horsehoes to get more completion (boring). There are side missions, but they are very un-exciting, such as the Quarry and 'delivery boy' jobs.
GTA: 4 - No gang wars and obviously no gang recruiting.
GTA: San Andreas - Gang wars and gang recruiting.
GTA: 4 - Police cars now have computers, which can be used to track down suspects in Liberty City, but also to target where crimes may take place.
GTA: San Andreas - No police computers in cop cars. You need to initiate "vigilante" to chase criminals.
GTA: 4 - No firefighter or paramedic missions
GTA: San Andreas - Firefighter and paramedic missions exist.
GTA: 4 - Underground ammunition stores sell you weapons. Friends have special abilities - they can sell you weapons at even cheaper prices, provide you with bombs and even re-arm you with men in times of need. You can take them out for activities like bowling, darts, 8 ball, drinking, clubbing or eating. As with GTA: San Andreas, girlfriends can be taken on dates to.
GTA: San Andreas - You must buy your weapons at an "Ammunation" gun shop. You don't have the ability to make friends or take them out anyway. Girlfriends can be taken out to places of interest though.
GTA: 4 - Smaller map with only 3 islands, harbouring a town on each.
GTA: San Andreas - Bigger and more diverse map, including the country, 3 cities and desert surroundings.
GTA: 4 - Dramatically less weapons.
GTA: San Andreas - A huge arsenal of equipment at your disposal.
GTA: 4 - Probably better audio and great plotline.
GTA: San Andreas - Slightly less effective sounds, but still an intriguing story.
GTA: IV - Radio stations suck majorly.
GTA: San Andreas - Radio is quite relaxing, there's quite a few tracks you can get caught up on.