This is definitely a trade with its pros and cons.
On one hand-even with Holliday not producing like he did in Colorado, he's still a huge upgrade in LF over the duo of Chris Duncan and Rick Ankiel. Good baserunner and defender. Gives Pujols protection in the line-up. He has been hitting well in July, and maybe a return to the NL and a friendlier hitters park will help him return to the close to MVP form of 06, 07, and 08.
On the other hand-they gave up a lot to get him. Wallace projects be an impact bat(there are questions about his playing 3B, he might be a 1B instead and that position is sorta blocked in STL). Mortensen could be part of a starting rotation. Don't know much about the OF they gave up. This could only be a 2-month(and hopefully playoffs) rental, and if they do re-sign him it'll take some big money(though they would of course get compensatory picks if he signs elsewhere). Holliday is a Boras client. The last time the Cards made a trade with Oakland they definitely got the worst of it, the Mulder for Haren, Calero, Barton deal. I imagine a rotation this season with Haren, Carp, Wainwright, Lohse, and Piniero and it makes my head hurt.
I have a feeling I'm gonna like this deal this season, but regret them making it a few years down the road. The pressure is definitely on for them to win now. They have a lineup that can move up from the middle of the pack with-
2B Schumaker 3B DeRosa 1B El Hombre RF Ludwick LF Holliday CF Rasmus(and probably Ankiel some too) C Molina SS Ryan
A good top 4 in the rotation that could win in the playoffs with Carp, Wainwright, Piniero(I don't know whats gotten into him but I hope he keeps it up) and Lohse. And the bullpen has been very solid with Franklin taking control of the closers role.
I'm more impressed by Izzy becoming like the 30th guy (give or take a couple) since 1900 to strike out the side on 9 pitches. When he's on, he's filthy and impossible to hit. Unfortunately for the Cards, the easly inferred corollary is also true...