Not sure its that useful but I played them when I was going through all the no deposit bonuses:
Games that seemed to have medium variance but quite big wins:
* Irish Luck
* Cherry Love (I got free spins that retriggered twice)
* La Chatte Rouge (Nice looking ladies too )
Game which is low variance - crap wins but good for grinding out:
* Skazka (some sort of Russian fairy tale thing with annoying music)
Iron Man and Hulk seemed really high variance to me, Iron Man especially.
They seem to have some new games out like X Men, Elektra and Blade but I haven't tried them yet.