I keep hearing he was able to bully people with his size... something he will not be able to do on the NBA level.
There aren't too many NBA guards who can match his strength.
More to the point, he'll be going up against better/stronger bigs if he takes it to the hole in the nba.
This has worked out just fine for guys like Deron, Rose, Westbrook, Wall, Wade. etc. I think He'll be just fine.
Most of them pick their spots or rely more on quickness than just bulling their way to the rim.
If you look at Derek Rose's statistics, he's actually not a very high percentage finisher at the rim (about on par with Rondo) percentage wise. He's not a good jump shooter either - his midrange percentages have been pretty poor his entire career, and his 3PT percentages have never been anything special.
The one area where Rose really shines is the rate at which he gets to the line (and hits his free thows), as well as the rate at which he converts and-1's (a stat which indicates an impressive ability to finish through contact.
Rose is a pretty strong guard, and while his quickness does allow him to get past his own defender, once he gets to the rim it's his physical strength and body control that allow him to be successful at finishing with contact. Similar story with Dwyane Wade.
I see very similar characteristics in Marcus Smart. He's not amazingly explosive, but he's still pretty athetic (he has a 36" vertical according to draft express, and his lane agility scores were excellent at the combine). I think he'll overpower the majority of PG's with his pure strength and size, while I also think his combination of strength/quickness will make him a very tough cover at the SG spot. Once he gets in to the paint, he has the vertical, length, strength and body control to finish with contact and to draw a ton of fouls. Once he gets to the line, he's also a decent enough free throw shooter to make the most of it.
Everybody looks a guard's scoring as being based purely on shooting and slashing, but people forget about post game. Deron Williams has been destroying opposing PG's in the post for years, often forcing teams to send a double team because very few PG's can cover him down low. Smart is pretty good in the post for a guard, and I think he'll create similar matchup nightmares as well.
The way I see it is this.
If Smart gets matched up a smaller, quicker PG (Paul, Wall, etc) then he's always going to have a big strength and size advantage.
If he's matched up against a taller PG (Livingston, Carter-Williams, Jamaal Crawford, Exum) then those guys are all skinny, so he's always going to have a big strength advantage.
If Smart gets matched up against a quick SG (such as a Monta Ellis) then he's almost always going to have the strength advantage.
If he's matched up against a SG who is both bigger AND just as strong (Joe Johnson) then he's going to have a major quickness advantage.
The only case I can see where Smart may struggle is if he's up against a guard with similar size and strength to him. Of the top of my head I can think of maybe four guys that fit that description - Dwyane Wade, James Harden, Deron Williams and Lance Stephenson. To be honest, I think Smart has the strength, size and quickness to give every one of those guys a hard time.
Offensively I think he'll be very nice. I like the fact that he's a guy who will attack the basket with wreckless abandon, and will score a ton of points in the paint and at the foul line. I think this team has desperately needed that every since Pierce left for Brooklyn. Not only does it give you high percentage points, but it also puts a ton of pressure on the opponent's interior defenders and increases the chance of getting their bigs in foul trouble. That then forces opposing teams to collapse the defense and run with a more 'zone' like defense, which opens up the perimeter for guys like Bradley, Green, Sully and Olynyk.
I also don't think his jump shot is broken. I think it certainly needs improvement, but there have been a lot of guys who came in to the NBA as mediocre shooters, but improved over their careers. Certainly not a given, but I'm not going to judge a guys career potential based on his ability to shoot when he's a 19 year old rookie. He may improve or he may forever suck as a shooter. Either way worst things have happened. Dwyane Wade has always sucked as a shooter, and has still be one of the most dominat scorers in the NBA his entire career, despite playing the SG spot. The theory that "a SG who can't shoot = disaster" has disproven, just take a look at the three championship rings on Wade's fingers.
Defensively I think Smart has the potential to be the best perimeter defender in the league 2 years from now. In fact I'm more intrigued by a Smart/Bradley linup than I am with the Rondo/Smart combination. A backcourt of Smart and Bradley might be the best defensive backcourt the NBA has seen in over a decade, and Smart's ability to attack the basket (combined with Bradley's competence from outside) I think makes them a nice combination on offense too.
Plus those two guys running with Green in transition...scary. Just imagine a 230lb Marcus Smart running full speed at you - anybody who takes that charge is sure as hell going to be feeling it in the morning.