I just picked this up from Fred Meyer last weekend when it was $20, with the mindset that I shouldn't expect too many hours of playtime with the overall package. When the game was released, I wasn't happy to learn (like many others) it was essentially the Tanker/Virtuous mission labeled as a retail release, and I'm sure if the threads still exist here one could go find my rather negative opinions I shared there.
After playing it, there's a lot more to it than I initially expected. The 4 Side-Ops were surprising different, had unique voice-acting/briefings, and completely different enemy placement/pathing, in addition to their own cut-scenes. Think of it as playing different scenarios in a table-top board game, like Space Hulk or Pathfinder. Terrain traversal, like what objects you can get on top of, is fun to mess around with on its own IMO.
The Deja-Vu/Jamais-Vu missions are pure fan-service, which is a huge bonus for fans of the series, but if that isn't for you then you are playing the wrong game series.
Most of this is in direct opposition to my expectations. I thought there would just be a basic text dump for the Side-Missions, similar enemy/item placement, and uninteresting "hide behind the waist-high cover" stealth. I can honestly say there's a lot more to be had here than I'm sure most of you assume.
Is it a full-game? The content is far too piece-meal and disjointed weighed separately, but together presents a variety of well crafted, thought out, and interesting scenarios to play through.
Is it a demo? The amount of content, from a variety and quantity standpoint, far surpasses any demo I've play. There are numerous paths the developers put into the missions for you to find/try out, that are also interesting to find (some of which are required for a trophy/cheevo, btw).
Is it too high a price? At $25, I'd say yes. I bit at $20 because I figured it wasn't going to get any cheaper by the time my birthday rolls around later this month.
If you want to play it sooner rather than later, I'd look around for ~$20. Otherwise, I'd say wait for