Lacks the depth of SA, but makes up for it in other areas. A fantastic must-play game with tons of things to do and see.
Bad: Windows Live account needed, as well as the installation of Rockstar Games Social Club; high system requirements due to a poor console-to-PC port
Compared to San Andreas:
+ better selection of entertaining and funny radio stations (plus your own 'User Tracks' channel which SA had too)
+ more interesting side missions (non-story related)
+ improved GPS: you can now see the police 'quarantine' area you must escape and the map guides you to objectives, instead of just telling you where they are
+/- much better graphics, but more demanding and longer loading times
+ you don't lose weapons when you die, only when you get 'busted' by police
+ unique safe houses that 'feel like home'
+ much better audio/sound effects
+ better "feel" to weapons/shooting and driving
- not as large a selection of vehicles to drive
- less customization (e.g. character appearance)
+/- less mission variety, but still a good amount of variety (most missions are hitman-based, which I tend to like)
- lacks depth that SA has (e.g. no buying real estate, no working out at the gym to improve stamina and strength, etc.)
- less variety of surroundings (basically just the city and suburbs)
- not as large a city
+ more realistic
Overall: This was the first GTA that I had ever played. After this, I played San Andreas, hence I compared many aspects between the two. Overall, San Andreas has more depth to it, but GTA IV makes up for it in other aspects. If you've enjoyed any past GTA games, then you'll most likely enjoy this one. Try to play it on a console, as the PC requirements can be steep because this is a console port and was not optimized for the PC. As long as you have a quad core CPU though, you'll be okay.