Just got back from 30days(Panama canal and then Alaska) with the same roomie.
#1 Tip, find out if they snore even if your a sound sleeper! Dude was somewhere between a bear and a jetplane, and then gasped as if dieing. I don't snore so it didn't occur to me to ask, information that you should share if you know though!
Although I could have afforded it alone I probably would have only done the alaska portion solo. Would never cruise with this person again but I don't regret it. Fantastic trip, just ignored each other for the most part.
Will my next trip be solo? Probably, though if cost was a big issue I'd consider it. Just do some due diligence and ask questions beforehand. Worst case scenario there are 1999 other people to make friends with.