It's not that interesting from a scientific perspective. They're not doing anything that any doctor or biology grad student couldn't do. It's the concept that's interesting.

Food is a pretty inefficient thing. In terms of the time we spend consuming it and the resources expended in its production. Soylent is a first step towards a solution to those problems. The theoretical efficiency gain is very high. Of course, Soylent won't achieve that, but the idea is alluring.

Personally, I don't want to drink Soylent for all or even most of my meals. I drink it 1-2x per week. I generally feel better after drinking it than after eating a meal, and i'd say say Soylent is healthier than the average meal i'd make for myself otherwise.

Aside from that, it's fast, cheap, stays good for a long time and requires no cleanup. All that doesn't mean it's going to change the world, but it is a nice addition to my palette of available foodstuffs.