The first thing I did after reading this news was go to ESPN Park Factors. As of Dec 7, 2011 data, Busch Stadium was the 4th most difficult place to hit a HR, Angel Stadium was 6th. Not a huge improvement, but an improvement none the less. Looking at spray charts for Pujols we can see most of his power goes to left. The dimensions in Angel Stadium appear slightly less friendly to Albert than Busch was, in fact, looking at his spray chart at home and overlaying that with his new park is discouraging, as there doesn't appear to be any homers gained (as far as last season goes). It doesn't look like home park is going to be a boost to his numbers.
The last significant power hitter to switch leagues, Adam Dunn, didn't do so hot adjusting to AL pitching. That's not a fair comparison as Pujols is five times the hitter Dunn is, but we should keep in mind that going to a new league with new pitchers isn't an easy thing to do. Pujols is an exceptional hitter and i don't think this is something that we should have to worry about tremendously with him, but it's going to be there in the back of our minds. His power numbers should remain about the same, but a small regression in AVG shouldn't be a surprise to anyone.
Offense was a problem for the Angels this past season, as they were middle of the road in baseball in runs scored and home runs. While a team can get by on that, it isn't enough to keep up with the Rangers prolific offense in the AL West. Pujols is going to go a long way to providing more offense for them, Vernon Wells had a horrible batting average but still put up a respectable 25 HR's. Tori Hunter had an average average but still had 23 HR's. Trumbo will probably move to 3B and hopefully improve on the power he displayed this past rookie season. Power won't be a problem for this team now. There are also a lot of good OBP guys here, so even during the power droughts, they should still be able to manufacture runs the old fashioned way.
Bottom line, Pujols is Pujols and will continue to be so. Expect the power to remain the same, the AVG to drop slightly, and possibly his Runs scored to dip too. Albert had better protection in St. Louis with the likes of Holliday and a resurgent Berkman, but Albert is too good a hitter to let that affect his individual performance.