First off, by trading Alonso, that virtually demonstrates that the Reds will be committed to bringing Joey Votto back long-term. I kind of doubt that the Reds would trade away their insurance policy if they were not relatively certain that they could bring back Votto. That news should be very exciting because nobody likes to hear about their potential MVP candidate leaving.
However, Latos himself is a very good addition.
Latos is only 24 years old. Alonso is also 24 years old. They are not selling the farm in order to bring in a veteran for the short-term. Although Latos has been with the Padres for three years, he is by no means old.
Also, Latos has been pretty successful for these first three years. His career record is unfortunately tilted towards the losing side at 27-29. However, he had been playing for the San Diego Padres. They have virtually no offense, so his career 3.37 ERA has apparently not really been supported. He also has quite a bit of control as his WHIP currently sits at 1.15.
He definitely has top of the rotation potential, and now that he plays for the powerful Cincinnati Reds, he will most definitely get much more run support. The National League Central could now be much more interesting with the Reds making this highly significant move.