Complete Mage - the Reserve Feats change the pace of the game. A lot. In my Iron Kingdoms games the Wizard blowing through the bulk of his spells pretty much determined when the adventurers would hole up for a while. Generally the party would be around 3/4 to 2/3 on hit points.
Now the wizard is a lot more likely to save his spells and use Reserve Feats for the bulk of the minor encounters, saving the bigger spells for later. The part tends to be down to 1/3 to 1/4 hit points when they hole up, and is more likely to be the cleric who runs out of spells.
With the addition of a healing Reserve Feat in Complete Champion things will likely even out a bit, with the party running around looking like ground beef - the healing Reserve Feat maxes out at 1/2 hit points. So I suspect that I will see a lot of characters running around at half hit points for much of the game. This will make the melee monsters a bit more deadly, I think.
For my game I really like the changes, in the past there were a few occasions the party would miss out on stuff because they left, giving time for the bad guys to get prepared. But the changes are not for everybody.
The Complete Scoundrel - Tricks are kind of neat, I wish the players would do more with them, unlike Reserve Feats it seems like they forget that the Tricks are there. Complete Scoundrel is another good book, and I really like the title!
The Complete Champion - I got it for the Divine Reserve Feats. Not all that fond of it otherwise. It seems a bit thin on things I would actually use in my games. You can't win 'em all. I like affiliations, but they ate up too much room in this book, and they are not the affiliations that I am likely to use.
The Auld Grump