My first post on the Astros was Astros Offense On Record Setting Low Pace. Right now their OPS is .643 and the league average is .729. So .643/.729 = .882. That would be the 11th worst since 1969, as you can see from the table below.
They have been doing better lately. In June, the Astros had an OPS of .691 while the league average was .720. That is a ratio of .96. So far in July, it is .689/.733 for a ratio of .94.
The Astros have an OPS+ of 73 according to Baseball Reference. It takes park effects into effect as well as the league average (it is calculated a little differently than above). The lowest team OPS+ I found going all the way back to 1920 was 69 for the 1920 Philadelphia A's. So the Astros are close to that.
I am not sure what to make from the Astro's park ratings in the Bill James Handbook. For the years 2007-9, they have a run rating of 96, meaning that the runs scored in their park is 96% of the league average. But the rating for AVG is 101 and for HRs 108. So that indicates a slightly above average hitter's park. The walk rate is 98. That does not seem like enough to offset the HR and AVG ratings to say their park is a little hard on the hitters. The error rate is only 87. That might hold down the runs. My best guess is that when it comes to OPS, Minute Maid should be a little helpful to the Astros' hitters.
The Blue Jays have an isolated power (ISO) of .205 since their SLG is .445 and their AVG is .240. That is higher than the all-time record of .205 by the 1997 Mariners. Relative to the league average, it would be the third highest since 1900, at 138 (.205/.148 = 1.38). The league ISO in the AL this year is .148. The 1927 Yankees are the highest in realtive ISO at 153. My first post on this was Blue Jays On Record Power Pace.