Number of games isn't that important IMO [I would play as long as there are games I like, and just few slots are enough for me]. The most important would be both trustworthiness and bonuses. A good bonus is the main motive for me to move from a casino to another, if I get a good one I always give the new casino a try.
Regarding trustworthiness, not necessarily for the website to be x years old, but just consistent and no major issues, the owners are active and there is a "team" rather than a single person (and you could tell regardless of what the casino claims), I wouldn't be playing crazy there but would at least give it a try, and you get used to the casino with time and trust increases.