It takes a bit to get set up. But once you do, it's great for filling out bundle games you missed.

The way it works is you add the list of games you have available for trade. You sync your profile and it imports your wishlist. You can then manually add and remove things from the wishlist, and and and remove tradables.
Once you've got a list of your availables and a list of your wants, you can run Match on your Wishlist. That will show you the other users who both have something you want, and want something you have. You can Propose a trade, selecting things on your list and things on their list to add to the trade, then adjust quantities, like Any 2 of mine for 1 of yours, etc. and put an expiration timer on the trade. Then they can Accept the Offer or Reject the offer, or they can Counter with a different offer of their own. Almost all the time people will accept bundle game for bundle game trades with no problem. Other stuff you can negotiate on.

I would recommend trying it. See here 3 people have Cities in Motion available for trade.
See my profile for an example of Tradables and Wishlist, with priorities and additional properties filled out.