There's your problem mate. Cheats. Try playing the single player without them. It's very rewarding. If you do the missions, especially the assassinations, in the right order then you get all the money you will ever need. Then you can fuck about to your hearts content.
As far as online goes there's more than enough content to play online on your jack but I admit you do have to find the right server. Still, with all the heists, biker stuff, races etc etc around it's not that hard to find willing people to play online with.
The next 2 big Rockstar titles, Red Dead and the new GTA, will be very online geared as it's the way forward. There will still be a single player, it's what they do very well, but, like GTA online, content is where it's at baby!