Here's how Mookie Betts was rated according to MLB.com:
Hit: 60 | Power: 45 | Run: 60 | Arm: 45 | Field: 55 | Overall: 55
Basically, he's an above average hitter, who will be hitting a lot of singles and doubles, as he doesn't have a lot of HR power, which is not a good thing considering Boston ranks 15th in slugging percentage, with only David Ortiz showing any signs of power.
Unfortunately, hitters will be running on him, as he has a weak arm and mediocre fielding skills. He's playing OF because Dustin Pedroia is at 2B for the next decade.
Mike Trout he isn't.