Accessibility merely means that anyone, from saint to spawn of Satan, can join a game where you are having fun and either complain that you're being unfair to players with less experience or reflexes than you and/or find ways to sabotage everyone's efforts for their own pleasure, never mind the experience for other players.
While unrelated to the ease of play, I also echo several comments concerning guardians purchasing the game for individuals who clearly don't have the maturity to cope with it... or alternately, individuals without that maturity in the first place purchasing the game. It's simply GIFT all over again, applied via bullets: any normal individual, freed of consequences for their actions, may turn into a jerkass, for whichever definition of jerk/ass behavior you'd care to employ.
So no... I'd say not a reason to consider it the best. Besides... you still have to pay for it, right? TF2 went free a while back, so now that game doesn't even require someone put the monetary effort into accessing it. In regards to accessibility alone, I think it probably trumps CoD by requiring only a computer that can run the game, an account, and internet access (all of which you would ostensibly have ready for CoD already).