Completely agree. I went away on holiday for a week, before I was playing it every day, when I came back I didn't even think about it until now (4 weeks later).
This game just didn't have the longevity of the previous games.. I found I outgrew my city areas quite quickly, multiplayer was completely broken (whenever I clicked to join a game, all the lots were already full, I could never find a region with a free city. So I start my own region and nobody ever joins!) and even when I had a full region to myself, which is what I wanted all along, I could only ever link up 4 cities out of 16 because of how the Highways interconnect.
On reflection, I think one of the main problems was actually that the game was too easy! Plop in a Coal mine and a Trade depot and you could be making millions without ever plopping a house.
I'm just looking forward to GTA5 now... they've delayed the launch for 4 months to get it exactly right. Perhaps EA should look to Rockstar to see how to manager a cult game franchise properly... Attention to detail!