What have we learned after a little less than one week into the season?
That it isn't enough time to judge whether a team will be a boom or a bust, and performances in the opening series -- good or bad -- probably tell us very little about how a season is going to go for most teams.
The Cubs' offense, for example, is probably going to be steadier than it showed the first few games. And it's highly unlikely the Giants' pitching staff is going to combine for many shutouts this year, though after their first two games against the Dodgers, San Francisco's hurlers looked somewhat untouchable.
Our weekly Power Rankings are based on several criteria. While they will largely reflect positioning in the standings, we'll also weigh the big picture -- how we think teams will fare over the long haul, who they played the week before and who's coming up on the schedule, and which teams we suspect will still be in the playoff picture toward the latter stages of the season.
Biggest jump: The Mets improved from No. 14 last week to No. 11. We won't know the immediate answer to the question that the Mets seem to have to answer every year: can they stay healthy? But assuming they do manage to get through a season without losing a chunk of their rotation and have just a normal spate of aches, pains and injuries that every team deals with, it's reasonable to think the Mets may be a top-10 team at some point this season.
Biggest drop: The Blue Jays were in the top 10 in our opening rankings, coming in at No. 9, but landed at No. 13 this week. It's likely our panel of Power Rankings voters will have differences of opinion on the Jays all season, but if their rotation stays healthy and intact, they may be better than we think. They had a nice opening series with the Yankees, scoring 10 of their 15 runs in the seventh inning or later, which is impressive given the power of New York's late-game relievers.
Power Rankings Top 5, Week 2
1. Astros (No. 1 last week)
One time through, the rotation has performed as advertised. Including Charlie Morton's six scoreless innings against the Orioles on Monday, Houston's starters have allowed six earned runs over a combined 30 1/3 innings -- that's a 1.78 ERA -- so far in 2018. Starters have allowed 31 baserunners in the season's first five games.

2. Dodgers (2)
They had a bizarre opening series with the Giants, splitting the four-game set while allowing only two runs total. But the Dodgers were also shut out twice to open the season, and they scored 14 runs in the final two games. What does this mean? Probably nothing, except that it's way too early to start screaming about World Series hangovers.

3. Nationals (5)
The Nationals have yet to trail in 2018. They scored in the top of the first inning in each game during their sweep of the Reds, and also in their opener with the Braves on Monday, and have never let up in any of the four contests. Adam Eaton, whom they sorely missed last year when he was lost to injury early in the season, is off to a blistering start. In three games in Cincinnati, the outfielder had eight hits in 13 at-bats with two homers and seven runs scored.

4. Yankees (3)
A four-game series split with the Blue Jays to open the season didn't reveal much about how the Yankees' season will go, but it gave fans something to talk about. Manager Aaron Boone had his first controversy when his decision to intentionally walk Josh Donaldson backfired, and Aaron Judge also gained some attention simply by not hitting enough. The presumption is that over the course of the season, Boone will make sound decisions, and Judge will hit, a lot. From a big-picture standpoint, there was no reason to boot the Yanks from the top 5.

5. Cubs (4)
It has been a strange start for the Cubs, who have been either very good or practically invisible offensively, depending on the day. In their two wins, they scored 18 runs. In their three losses, they've scored once. They've also been shut out in consecutive games for the first time since last May 26-27. They were shut out by the Marlins, 6-0, on Sunday and by the Reds on Monday, in a 1-0 Cincinnati win. So, not a great start for the Cubs, but it's a safe bet the bats will break out soon.

The rest of the top 20
6. Red Sox (7)
7. Indians (6)
8. Cardinals (8)
9. Diamondbacks (10)
10. Angels (11)
11. Mets (14)
12. Brewers (12)
13. Blue Jays (9)
14. Twins (15)
15. Rockies (13)
16. Mariners (17)
17. Giants (18)
18. Athletics (20)
19. Rangers (16)
20. Pirates (N/R)