The game definitely becomes less difficult the longer you play.
I play conservatively when it comes to holding on to cards and managing the crossfire deck, but value offense over healing when it comes to black market purchases.
Some missions are better with 4 players, but 2-player works just fine in most cases.
Human is acceptable for all roles, and may be the only race (without upgrades) that could be used by all players at once without drastically lowering your chance of success.
That said, I like to play Elf most of the time.
My group wins more than half the time, but we lose or abort often enough to keep the game interesting.