Dellandrea is an easy choice for me here, but I am a bit surprised he's leading it by so much. There are a handful of other good choices (Olofsson and Sandin aren't far behind on my list). Based on my viewings, Dellandrea is just a "good at everything" type of player. He doesn't have any extremely high end skills, but he's good to very good at pretty much everything. There really aren't any holes in his game. Pair that with the fact that he doesn't have much of a supporting cast on Flint, which inevitably leads to lower point totals, and that he's one of the youngest players in the draft, and it seems like he's a prime breakout candidate next year. I have him around the 20-23 range in my rankings.
Regarding Nordgren, the big knock on him based on the reports I've read is that he's not a very good skater, which doesn't usually pair well with smaller players. There are a few exceptions in the NHL, but not many. He has a ton of skill though, and he put up some pretty crazy numbers this year, so I'd be happy with him in the 3rd, or maybe 2nd depending on who's still on the board at 45.
Edit: I like the Thomas comparison a lot. Not necessarily stylistically, but more based on the circumstances of their draft year. Both went into the draft as very well-rounded players, good at everything but not necessarily top-tier at anything, late birthdays, lower point totals potentially due to the dynamics of their respective teams (Thomas trapped behind older, more established players, Dellandrea stuck on a poor team with little surrounding cast). Obviously not saying Dellandrea is going to break out anywhere near to the extent that Thomas did this year, but there are a lot of parallels that can be drawn between their situations leading up to the draft.