You're seeing this from the "Obama sucks" perspective, which is a totally valid perspective to have. NK likely sees this from a "OMG, you're allowing US troops to invade our country for something simple like food" perspective. Because that's valid too.
That's always been the crux of these deals, of which there have been quite a few over the years. They tend to break down like this:
US+NK: Ok, food for stopping the project, deal.
NK: Ok, stopped. Where's the food?
US: No food until you prove you've stopped.
NK: How can we possibly prove anything to you when we both hate and distrust each other?
US: We're going to send some "observers" (read: armed troops) to your country to 'inspect'. You have to allow them to go anywhere in the country, including any top secret military bases. We're going to remember anything they discover and will of course use that information should there be a war. And if you try to stop our observers from doing anything they might want to do, whether it's part of the agreement or not, it'll potentially be an act of war.
NK: That sounds like an invasion to me, and we'd prefer not to be invaded and conquered thanks.
US: No inspections, no food.
US+NK: Ok, deals off, no food, no stopping.
The only difference between previous deals and this one is that the US has pre-listed the places they're going to send the "observers" and NK has pre-agreed to those places so this deal has a greater than 0% chance of actually occurring, unlike every other deal (except Kaesong of course, which also succeeded because it was geographically limited).
Is it worth risking the chance that NK could hide weapons development just to have one single diplomatic success in NK where every single other one was doomed to failure before the ink was dry? Obama thinks so, but I can see how people who believe we should just "conquer the country and damn the consequences" would disagree.