They're not all that different to the versions included in Triple Deluxe, so if you've played that game you'll know what to expect.
Kirby Fighters is surprisingly fun and the the eShop version adds quite a bit of content--boss fights, extra modes, new stages, unlockable skins for each copy power, etc. Multiplayer is still local-only, unfortunately, and the two new copy powers are only unlocked if you have Triple Deluxe save data on your system.
Dedede Drum Dash is pretty shallow and doesn't have a lot of content; the eShop version adds some stages (plus harder remixes of every stage) and some new gimmicks but I still don't think it's very interesting. There are some aesthetic unlocks but they're almost all tied to having Triple Deluxe save data on your system.