Having Flash is a huge bonus for timing and interaction, letting you get something out of the way when your opponent might need it most to affect you
It covers Commanders from every color
The card was perceived as unremarkable, so it was buffed to provide a +1/+2 bonus
In my opinion, good Rares makes opening packs even more fun, since there is a realistic chance any pack could contain a Standard staple, not just the one-in-eight packs that happen to contain a Mythic
Its also a rather brilliant (though divisive) marketing technique, as people who might not normally have paid $20-$30 for a collectors booster pack might now buy a few (or a box) in the hopes of opening such a special card
Additionally, some cards, due to their synergy with other cards, can form deadly combos, giving one side an unfair advantage