I've said this before, but: I still don't like interleague play, but I have liked the way that it added the the structure of the season, sort of like the way the All Star break puts a marker in the middle of the year.
I'll miss it next year when it's gone, and the season will really not have any natural rhythm.
In the old days, when I stared really following baseball, the road trips gave the season some structure. There were natural swings, natural trips: for the Giants, there was Montreal/New York/Philly, Chicago/St. Louis/Pittsburgh, and within the division Cincinnati/Atlanta/Houston. The normal schedule was to do one of those groups combined with a homestand with those teams. It wasn't always completely that regular, but it was close. And usually you would stay within your division in April and in September.
Let's see...how about 1973, a (false) promising year. Hmmm..actually, they started with the East on April 24, with a road trip to the Cubs and Cards and then a homestand with the Pirates, Cubs, Cards. See? They got the trip to Three Rivers in later, at the start of a trip that then went Expos, Mets, Phillies, which was followed by an Expos, Mets, Phillies homestand. So it wasn't 100% regular, but it was mostly variations on a theme, if that makes sense. That same Pirates, Expos, Mets, Phillies road trip came back in August, with the last game at Philadelphia on August 29 also ending the interdivision schedule. All of September was within the West; I'm not going to look, but that was generally true for everyone, every year, during the 6/6 configuration. You knew that you were going to do both of the home and away marches through the other division twice (that is, two homestands and two road trips with each group of three), and it was very easy to keep track of what you had done yet and what you hadn't.
That was lost in the AL when Toronto and Seattle came in, and eventually it was lost in the NL as well. But at least the interleague interludes put some structure back in. I don't know; maybe I'm the only one who likes it. But I really do. 162 games is, of course, a long season, and it's nice to have some regularities, some markers. It was also nice to have some clue about what teams might be coming up next; now, the schedule always seems totally random to me, just one series after another, and it'll (as far as I know) seem even more that way next year. Plus, of course, with everyone in five team divisions, it will be impossible to stay within the division in September. Then again, with Selig adding WCs all over the place, who knows whether your division rivals will even matter in September (although for teams having bad years, at least divisional play allows for the fun of being spoilers against real rivals, so that won't be happening much either. Hey, Red Sox fans; if you're having a bad year next year, maybe you can get to play spoiler against some random National League Central team in the last week of the season! How fun!).
Seriously: I'm sure part of my bias here is towards the structure I grew up with. But, again, I'm not asking for that particular structure back; I just want some sort of markers throughout the season.