It's really hard to say whether the NX will be competitive for a few reasons.
First, Nintendo hasn't released many details about the NX, so we can't really make and apples to apples comparison to the PS4/Xbox One. Nintendo said that they didn't reveal the NX at E3 this year because they are trying something new and they didn't want anyone else to see it and copy it. Whether this "new thing" is a game changer that puts Nintendo back into the major leagues of gaming remains to be seen. It could be something that catches on and helps sell millions of consoles, like the Wii Remote, or it could be something that increases console costs and is met with an overwhelming "meh" like the Wii U tablet controller.
Secondly, Sony and Microsoft are about to move the target. Both have announced updated consoles that will have improved hardware. We don't know exactly when the PS4 Neo and Xbox Scorpio will be available, but they could well do the the NX what the PS4 and Xbone did to the Wii U...make it obsolete almost immediately after release.
Finally, there is one thing to always keep in mind about Nintendo: they make excellent 1st party games. With more powerful hardware and games like a new Legend of Zelda to kick off the NX, it could be successful because of a few console selling software releases. I've personally thought about getting one because of Zelda, and if they offer some other unique and interesting titles such as a new Metroid Prime or Endless Ocean, I would probably bite. Also, don't underestimate the appeal of Smash Bros. and Mario to many gamers.