For quality, playability, difficult, replay value, and cute factor. This game gets my vote.
The first thing you notice is the graphical changes made over the original Megaman. Getting past their overwhelming cute, "chibi" style you'll realize that everything is incredibly well done. From the way Megaman runs in a bouncing over the top style, to the overdone motions of the bosses, to the stunned look defeated enemies give before exploding everything is gorgeously rendered in 3D-in-2D style. The stages are gorgeous with platforms, walls, and backgrounds given a sufficient amount of animation to make it interesting and not too busy.
The controls are spot on. Megaman moves, jumps, and fires responsively enough and the special weapons you collect as you defeat each boss really do help in a number of situations, so you'll find yourself swapping from Thunder Beam to Rolling Cutter to Hyper Bomb regularly in a number of situations. Playing as the bosses is one of the great reasons to pick this game up and while they aren't equipped to handle very stage and obstacle perfectly (Bombman and Cutman will drive you crazy in some spots) they are fun challenge and a wonderful addition.
The music is fun, upbeat, and doesn't detract from the experience, rather adding to the cute, happy theme. The voices are the real shining point of the sound, however. From Megaman's adolescent concern to Elecman's pure arrogance the voice actors were wonderful (Elecman saying "Energize" will get a groan from a lot of anime fans). Although if you're already groaning at the cuteness, the voices won't help at all.
The replayability of this game is phenomenal. There are 100 challenges, three difficulties, and 11 different characters (8 bosses, Protoman, Roll, and Mega) to play as. If that's not enough for you can shoot for speedy times, higher points, and more enemy spheres collected. But wait! There's more... you can build your own Megaman levels. For all you fans of the series who have always wanted to design your own level, here's your chance. After collection Terrain and Enemy packs from the actual levels (some of which require some thinking to do so) You can enter the level creator and have fun. You can make stages, play them, and when you want to share your masterpiece with the world, you can upload it onto Capcom's dedicated server. Also on this server you'll find other people's stages (for good or ill... be forewarned. Some people have no clue what they're doing) as well as other content (like Roll). This server also opens up the opportunity for further expansion with different playable characters (Dr. Light? Dr. Wily? A Hardhat?) So you'll get maximum play out of what could've been a short, quick remake. Kudos Capcom.
The system isn't without its flaws however. There are a couple of areas where you'll get that classic NES slow down. If this is intentional to "preserve" the game or its just a by product of a lot of figures, I don't know, but its annoying at times. Also, the game can be maddeningly difficult. There are three difficult settings to help this, but trying to go through some stages on hard is equivalent to drinking gravy on the number of years it takes off your lifespan. As I mentioned, some of the bosses aren't particularly cut out for every stage, but the challenge is nice.
Overall, I highly recommend Powered Up! to both veteran and new Megaman fans. The vets will find a game that they can keep coming back to over and over and the new fan will get the best of everything Megaman has to offer in an easy to access package.