I didn't mean to sound rude by the previous comments, I do know that you're a newcomer. Welcome to the game!
In my opinion, MP is the heart of the game. I enjoy outsmarting and outmanuevering opponents seeing novel strategies tried out against me. Even fighting a losing campaign is fun against an intelligent opponent.
That being said, there is definitely something to the single player game. A lot of the players here will swear by it, and there are some good mods that have been and will continue to be released for it. You will just have to make the most of your gaming experience within that realm until you get a high-speed connection. If that takes years, I think you just might continue to play SP on until then. It's a damn good game.
A good starting point for you to make the most out of your SP experiences is the Wiki. Go to hoi2.nsen.ch
It contains guides, references, and links for the newcomer. It can even get you started on developing your own modifications to the game, to strengthen the computer against you and improve the atmosphere of it to your tastes.
Make a note of the links to the Historical Stony Road mod, the Total Realism Project, and the CORE mod. These are the homes of the premier mod development teams in our community.
Again, I'm sorry for your predicament, but welcome to the community!