It's a valid complaint. The background strings sound like someone picked up some instruments and started hitting entirely random notes on them, and the fact that there are actually segments in the song where that's all you can hear is a pretty terrible decision on his part.
As for the rest... it's hard to argue those sorts of things, but really, if you want to convey solitude then using a complex composition that uses a large number of instruments playing more or less over each other and vying for attention within the composition isn't a very good way to do it. That sort of thing requires subtlety, something that the piece you linked lacks almost entirely (particularly around the middle of the composition, where the music swells a ridiculously excessive amount). As for bliss... that's much more vague and hard to address, but the best I can say in response is that I'm not feeling it. At all.
EDIT:
Which other instruments? Go listen to the three songs linked. I've skimmed through all of them, and I haven't heard anything but strings in any of them.
Not really, no. They can, but only when that beauty and excellence is driven towards doing so, which isn't always the case.
No, I've spoken to a lot of people about it, and emotions are never mentioned until someone points out that there is none. The same's happened in this thread: no one made mention of emotion or atmosphere in Soule's music until people started pointing out that it isn't there. Hell, more than half the people who LIKE his music are agreeing that it lacks emotion.
And actually... well, look at the piece that you've linked and that you've specifically talked about. Look at the comments under it. I went through ten pages of them, with the only person mentioning any emotion whatsoever saying that it made him feel "terribly sad" when he hears it at the office... which is the exact opposite of the "bliss" you said that piece makes you feel (and, given the piece's title, bliss is probably not what Soule was aiming for).