This is interesting. For years I've blended together various ingredients (mostly stuff like broccoli, lentils, sweet pepper, ricotta, canned tuna, olive oil, various grains and nuts such as flax, sesame, hazelnut, sunflower), balanced these for macro and micro-nutrients using cron-o-meter, further optimized along various axes such as cost, taste, ease of use, ease of preparation, packaging, cleaning up etc. Food is primarily something I do to feed myself in the end, and I dislike it when there's too much fluff.

I'd be more wary of mixing together purified/refined nutrients though. Just as licking iron bars won't provide you with your daily needs for iron (elemental iron isn't very soluble and your body wouldn't be able to assimilate it well), there's more and more evidence that whole plants and animal parts contain more than just the usual nutrients, and that this particular mix may be needed to stay in good health - and conversely that substituting multivitamins and refined macronutrients for normal food may run the risk of missing some essential, complex interactions/packaging that occurs in it and which changes the way your body assimilates it.

Now of course, many people eat junk food and still live to be 60-70 so there's some leeway. We'll only really know whether Soylent is healthy enough (like, for someone interested in life extension, and not just satisfied with a classical life span) if this experiment goes for decades, and if it's done using more people, controlled conditions, etc (in short, using Science).