Most of the cards that say "You win the game" in the rules text never see play since unsurprisingly, that effect typically comes at a steep cost. Approach of the Second Sun may be the best such card ever printed since seven mana isn't an unreasonable cost to pay and finding the second copy is fairly easy in a control deck that can churn through seven cards in a turn or two. When combined with the life gain to keep you alive, the card becomes a nice, self-contained package of a win condition for control decks in Standard.
But what about outside of Standard? Modern control decks have been performing well recently, with Jeskai Control taking the top two slots of the most recent Modern Open among other top finishes and U/W Control finding its way into the format as well.
Approach fits best in the U/W shell since the Jeskai variant likes to both play consistently at instant speed and have some form of pressure from creatures, so its burn spells are a threat to end the game that the opponent has to worry about.
Most U/W lists win with an assortment of planeswalkers, mostly of the Gideon variety. Gideon of the Trials can lock down a threat early until you're ready to turn the corner, and big poppa Gideon Jura locks down several threats at a time and attacks a little harder. However, both of these planeswalkers can be liabilities if you fall behind by too much. If they get attacked down in a turn or two, then you're down a card and may have trouble closing the game out even with a pile of card advantage.
Approach of the Second Sun trades early functionality for a more robust win condition and some built-in inevitability. If your opponents are expecting to play a twenty-turn game and configure their deck as such, they'll be in for a rude awakening when you end the game on turn 10 while they have a hand full of threats they were holding to play around your sweepers.
Of course, playing more aggressively to race the inevitability of Approach just makes your sweepers more effective, which is the power of the card on a strategic level. It completely invalidates the way most strategies adapt to playing against control decks, particularly in Modern where Dispel is a much more common sideboard card than Negate.
And if you're afraid of counterspells, Boseiju, Who Shelters All does a great job of forcing your Approach through. That and the increased emphasis on cantrips are all the concessions this list made to accommodate Approach of the Second Sun, and I don't think it needs anything more. There's no need to go overboard when the card already fits so naturally in a control shell. Approach is powerful, simple, and seamless--all things I look for in a win condition. So stop putzing around and just kill them already.