So this is my "scouting" report on Hagens after watching a ton of BC games this year. I think I'm pretty objective about him, because the Caps obviously won't be drafting him.
Hagens has been a top 6 C all year. His 5v5 production has been excellent although maybe not elite. He has been on PP1 most of the year, with a short stint on PP2. BC's PP has been bad (and worse when you consider the talent), but I put no blame on Hagens for that. He doesn't really PK, but that's because the coach tries to spread out opportunity and not because of Hagens' performance, as he was solid in the short amount of time he did PK.
So one very common misconception is that he's played the whole year or even most of the year with Leonard and Perreault as his linemates. This is not accurate. The line with him, Perreault, and Leonard never brought out the best in either Leonard or Hagens. So while he's had a lot of games with them, he's also many other line combinations. The best was probably Perreault, Stiga, and him (which has been broken up for reasons I strongly disagree with but nobody asked me).
(For the record, the Perreault-Hagens-Leonard line is not a bad line. With that much talent, they'd have to be actively trying to be bad. But it doesn't take full advantage of their abilities and may even (slightly) hinder their development. And Greg Brown knows this, because he broke them up in the first place!)
His biggest strength is his hockey IQ. He's an excellent playmaker. His shot is solid. He's a very good skater. I'm not sure if any of his skills are elite or if the combination will be elite, but I expect his play to translate very well to the NHL after another season in college. He is a natural center in almost every possible way to the point where I worry that his game won't translate to the wing if an NHL team chooses to start him there instead of at center.
Hagens' biggest weakness is his lack of strength. (He's tall enough at 5'10.5 that I'm not that worried about his height in isolation as a forward.) This manifests because he tries to get to dirty areas on offense but then (sometimes) fails. And he's in the right position (generally) defensively, but loses battles because he's mostly playing against 20-25 year old men. But his instincts are all spot on. He wants to get to the middle of the ice, and he knows where to be defensively. And instincts and hockey IQ are much, much harder to change than the lack of strength from a hardworking 18 year old.
As a result, I strongly believe Hagens has the highest floor in the draft. I have a very hard time seeing him as anything less than a good 2C, because even if his offense doesn't pop at the NHL level, it will be solid, as will his defense.
His ceiling is less clear. I still believe his ceiling is that of an elite 1C in the NHL, getting 90-100 points yearly plus very good but not quite Selke level defense. But I get why people worry about the lack of upside given his offensive production this year.
In general, I've seen enough "special" plays that I feel like odds are in his favor of hitting higher offensive potential and becoming a very good 1C.