I'm going there. It'll be my 2nd time going.
It's held at the same location as Ohayocon, but it's a smaller con compared to Ohayo. By smaller- If Ohayo can gain 10,000-12,000 in attendance, expect to see 3,000-4,000 at Matsuri. If I remember correctly- The dealer's room was really small. Still a good number of dealers for Artist alley though.
If I were to rate it- i'd give it 3 out or 5 stars.