Only two issues I have with him as a prospect:
1. He is more of a strider than a quick/agile player. The RAC statistics may be a little misleading here because most of his RAC is just from raw sprint speed. For a lighter WR, he's not really an agile, shifty guy in space. He's more of a one-cut-and-go type. This is where I see a little bit of the Ted Ginn comparison people make. Ginn was even leaner and more linear though, so I think Ruggs is the better overall athlete. He also has better hands than Ginn. However, he's definitely not Tyreek Hill or even Tyler Lockett when it comes to foot quickness/suddenness. This could cause some issues creating separation, but I don't think he's bad in this department. Just not elite.
2. He has a somewhat lean, weak frame. He can be pushed around and bullied. He doesn't have much play strength. You worry about him taking hits. When you combine the lack of elite fluidity with the thinn-ish frame, you get a questionable skill set for possession situations. We know he'll be able to get deep, but will he be able to move the chains too? That may determine his ceiling. I think you're looking at an 800-900 yard player just on bombs and big plays alone, but can he add to that with some gritty possession work to become more than a feast-or-famine FF WR3? That may be the fundamental question here.
In conclusion, not a bulletproof guy, but perhaps a bit underrated when you weigh the draft slot vs. the rookie draft ADP. First WR selected. Falling to the 9-12 range of PPR rookie drafts from what I've seen. I think this is a tough first round rookie WR class to parse, but it's hard to say he isn't a solid gamble at, or maybe even above, his ADP. I'm personally fading Akers and Swift ahead of him unless it's a mandatory 2RB league and I'm starved for a body there. Do you take him ahead of Reagor? Jefferson? Jeudy? Lamb? That's where it becomes murky for me. I'd start considering him around the 1.05-1.07, but it's a tough call that high. I don't have a clear favorite there right now. When he slides to the 1.10 or 1.11 and those other guys are gone, I'm very comfortable taking a chance on him.