Gamer here. The reason people hate the SHIELD is that mobile games pale in comparison to games for dedicated systems. Having existing android games is a great idea, but it assumes that they work well with game pad input. Since most phones don't have physical buttons, developers have to create for the touch only interfaces if they want to be successful. Sure, you can do virtual touch buttons, but the best mobile games get away from buttons and instead use some form of gesture or swipes to control things. They take on a different form than the types of games you play on a 3DS or Vita.
The other reason that the SHIELD isn't going to work out is the price differential. You make a point about making back the difference after a few games. To me, that isn't really worth it. The best of Android gaming comes nowhere close to some of the even more mediocre 3DS and Vita titles. The average Joe might not tell the difference and be perfectly content with the games on their phone, but they also are not the target audience for this device. A gamer typically expects a higher production value and game structure that is not feasible to support on a mobile platform. People expect $1 / freemium games, so selling a larger game at a higher price that more accurately covers its production costs is a death sentence.
Angry Birds is actually a great example of how games monetize on various platforms. In the app stores, it is going to cost $1 max, because people generally aren't willing to spend more. This is the price that the market has decided on, mostly based off of the pricing models set by Apple. Now, to make more money off of the user, they will provide various forms of DLC, whether it is a set of levels or simply letting to skip a level. The console versions of the game, which function exactly the same, will cost about the price of other games for that console, potentially a bit less to set it apart. Still, they will charge at least 20x the entry cost of the mobile app, based on pricing expectations and what the market will allow.
The SHIELD has an issue here because it doesn't fit squarely into either pricing scheme. It is a capable device and could deliver gameplay comparable to that of the 3DS or Vita. That said, it is building off of Android which until now consists of mainly throw away games. The only real chance Nvidia has with it is to put money out there to get some higher end games on it. Otherwise, gamers like me aren't going to spring for it to be stuck playing what amounts to glorified flash games that were free and everywhere only a few years ago. At least with the 3DS and Vita, gamers know that they will be able to play titles from Nintendo and Sony. They have a reputation built up with their previous games, and we as gamers know what to expect quality wise. The SHIELD has none of this. There are no titles to sell it, nor have there been any promises of studios working on anything worth experiencing.
These are the same people that freaked out when War of the Worlds was first broadcast....
When did all of those elderly Americans move to Britain and start using twitter?
...though his invention worked superbly -- his theory was a crock of sewage from beginning to end. -- Vernor Vinge, "The Peace War"