This was tough. I had to go with Space Hulk: Death Angel because of solo play. I would have picked the Lord of the RIngs: LCG or Dust Tactics, except moving to New York City I am not going to have a gaming partner for a while.
LOL. I think that if LOTR is a co-op game then it should have a solo mode of some variety. And yeah, tough is one word for it, impossible might be another. I'm tempted to say DQ but as I technically already own it... It's such a hard decision!