The Nintendo Wii U ended up largely being a disappointment, especially for company sales, and with the exception of loyal fans. So the first thing you can expect from the Nintendo NX is that it's not going to be anything like the Wii, Wii U or other traditional gaming consoles. For starters, instead of viewing the NX as another platform in and of itself, it is going to be the future of Nintendo for all games the company produces here on out, which means hardware isn't as much of a factor. Additionally, instead of there being a console system and a separate handheld gaming system, the two are united as family so to speak, brother systems, and this was straight from the mouth of Nintendo's former CEO. 
According to Square Enix, you can expect to see both DragonQuest X and XI as games for the Nintendo NX. Furthermore, one thing fans want to see is a better release schedule for games, which Nintendo has no doubt taken note of for future reference. It's being rumored that the 4th platform for Ready at Dawn might be the Nintendo NX. Backwards compatibility for games is also a speculated feature, and it is also expected for Nintendo to have an online infrastructure that is highly competitive. 
Nintendo has been losing users for awhile now, and of course developers have subsequently been dismissing the company. However, it is quite apparent that developers are showing a huge amount of interest when it comes to the Nintendo NX. There might even be a new Metroid Prime game! People are also wondering about the Legend of Zelda game, and if Nintendo held off to just slate it for when they release the new NX system.  One thing for sure, you can surely expect the controller not to be quite so large!