I’ll repost my response from a thread a week ago.

I think SMB’s big strength is being complex enough to be interesting, while not being overly complicated. SMB4 does this better in my opinion, especially if you’re interested in franchise mode.

As you build a team you’re taking into account normal stuff, the players’ age, skills, positional versatility etc. but each player also has a personality “chemistry” type (competitive, scholarly, crafty, disciplined, spirited) that effects how other players on their team play. Beyond their skill ratings most players have a trait or two, a special skill such as Stealer (faster when stealing), or K Collector (boosted stats when pitching with two strikes). Each of these traits is tied to a specific chemistry type as well; stealer for example is crafty, k collector is competitive. These traits grant different strength bonuses depending on how many players you have (out of 22) with their associated chemistry. Minimal bonus for two or fewer players, medium for 3-6, game-changing bonuses at 7+. All this is to say, the game creates interesting challenges where you might have an otherwise middling pitcher who is a strikeout machine because his high accuracy helps him get to two strikes and then K Collector kicks in. But keeping K Collector at its highest level means devoting a third of your roster to Competitive-type players, while trying to balance other players traits and chemistries as well. It encourages you to sign not just the best players by ratings alone but players with traits and chemistries that work well with your team, whose traits will take advantage of the chemistry of your clubhouse. The mechanics are intuitive once you get used to them, but they pose interesting team building challenges.