I'm a seller on Discogs, so first I will note that many of the 1-star reviews for Discogs are disgruntled former sellers who couldn't be bothered to set up their store for automatic shipping prices - something buyers at practically any other online marketplace would naturally expect. The current 63 million item listings suggest that the sellers who remained were able to figure it out, and that includes myself.
Overall, you won't find a more outstanding and complete database of music anywhere else, and it only gets better by the day. This alone should merit at least a '3' in anyone's book.
But look, some folks have gripes about the attached marketplace. I get it, from both the seller's and buyer's perspective. But the bright side is that it's fairly straightforward to size up a seller before one buys. A buyer can read comments from previous buyers and make a good judgment. Is some seller feedback removed that shouldn't be? Yes, and it's usually because of Discogs' idea that the buyer and seller should communicate before negative feedback is left. Some will understandably disagree with this approach.
As for whether a buyer would have an overall good experience on Discogs, I can only refer to my best friend who is a collector and major buyer there. He runs into issues with perhaps 10% of the sellers he's not previously acquainted with, and these tend to be mislistings or incorrect gradings. He thus tends to gravitate to buying from particular dependable sellers. I wonder if there's really a music marketplace that can deliver results any better than this.
I honestly do think Discogs deserves a 4 out of 5 overall to say, yes, it's not perfect and aspects can be made better, but what's there is quite amazing and works well most of the time.