Not only that, but Assault Formation has two other things that it can do, too: allow a creature to lose defender for a turn for G, or have creatures you control gain +0/+1 (essentially +1/+1) until end of turn for 2G.
Right away, this card instantly makes popular creatures like Hornet Nest, Sylvan Caryatid, Courser of Kruphix, and Siege Rhino better. Hornet Nest essentially becomes a 2/2, Caryatid a 3/3, Courser a 4/4 and Rhino a 5/5. It also makes Nyx-Fleece Ram, a 0/5 Enchantment creature from Journey into Nyx, into essentially a 5/5 beater. It also makes a Limited favorite like Jeskai Barricade, a 0/4 defender with Flash that can save one of your creatures from removal, into a 4/4 that has the ability to lose that defender thanks to Assault Formation.
There are plenty of other creatures that benefit from this effect, as well. Crater Elemental from Dragons of Tarkir is a 0/6 for 2R that may have trouble seeing Constructed play, until you consider this card. That card has the ability to become an 8/6 beater for 2R, but only if you control creatures with power 8 or greater combined already. With Assault Formation, you could potentially have a 6/6 for 2R on turn 3 in a Red/Green deck, due to Elvish Mystic and Sylvan Caryatid providing mana ramp. Obviously, the set design team had this in mind when that Elemental was created.
There are countless other creatures even in recent sets that work well with this card. The one that should definitely be mentioned, however, is Ornithopter. Being a 0/2 flyer for 0 mana is already good, but to have a free 2/2 flyer is sort of silly. Then when you consider you can pump your whole team with Assault Formation, too, having some free flyers that can suddenly deal 3 a piece is quite scary.
As with many Enchantments, though, in Constructed you may end up with dead copies in hand. Still, the effect on Assault Formation is powerful enough to warrant trying to build around it. Whether this card will help create a stable archetype good enough to compete is another question. Considering there are cards in Modern that make this card even better, such as Wall of Omens which draws you a card, it's possible that this card could become more than simply a Standard-playable curiosity.
Of course, Doran the Siege Tower decks will be happy to include Assault Formation as a duplication of Doran's effect, but also enjoy the benefits of the other two activated abilities. Now Wakestone Gargoyle and Rolling Stones dsn't have to be the only ways to shut off Defender in that deck. Even better, Assault Formation allows the Doran ability to spread into different color combinations, allowing for big red and blue creatures to enjoy the benefits, although it's hard to say which Commander decks would benefit from this card. At the very least, it will at least make Doran decks even more consistent.
It's always fun to see a Constructed-playable Enchantment that could do real work in competitive play. Players are quite excited about this one, competitive and casual alike, and so am I.