Poulin's play style has been pretty well established since he was drafted, he's a jack of all trades type of guy in the Saad mold. The only debate there is really his upside, but I think his play style is pretty well understood. A super well rounded guy with good size but mediocre skating.
I think people are down on Poulin because he didn't hit the sky high expectations people had for him in his rookie year, but he did have a strong finish to last year in WBS. From January through the end of the year, he had 12 goals and 30 points in 51 games while playing center (as far as I know). WBS is also pretty starved for offensive talent, their top scorer last year had 42 points and they were in the bottom third in the league in total goals for.
I don't think there's a huge difference between POJ and Poulin in terms of upside, both guys project to be more of depth players than anything at this point. Poulin projects as more of a jack of all trades 3rd line C/W with mediocre skating while POJ projects more of a #4 transitional defenseman with no special teams upside. I think those upsides are fairly comparable.
As an aside, I think I agree with Pronman that the best Penguins young player at this point is Smith. Smith has POJ's NHL readiness with a clearly defined higher upside. A lot of the Penguins prospect pool is filled with near NHL ready, lower upside guys like POJ and Poulin. Smith actually has that upside though, even with his defensive shortcomings.