[quote name='Abalistar']My one concern with the game... Will I lose a lot of the value if I'm not playing online? I lack broadband, so I'd have to be purely solo.

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You will be missing out on some cool aspects of the game if you are not online.
When you are playing along and you are online but in your own game by yourself, you will come across blood stains where
other players have died. When you click on the blood stains, an animation will pop up of the players' last moments, so you can see what they were doing as they died. It will hopefully give you a hint so you can avoid the same death.
Another online perk is the ability to see scripted "notes" on the ground in your own game left by other players in their game. Hopefully the notes give you hints as to what to expect next, like maybe monsters hiding ahead or whether you need something special to progress. You can rate the notes so the good notes stay around longer to help other players and high rated notes give the person who left the note some health.
Additionally, as you play you will see ghostly figures of other players as they are playing the same area as you are in real time but in their own game.
And of course you will miss out on multiplayer stuff like PvP and joining another person's game or summoning help from other players to go through a level.
The online stuff is really well done. There is no voice chat but the way everything listed above is handled voice chat would take away from the overall game.