My LHS just got done building one of these with a Castle 3800 brushless motor in it and the thing tears up! What bad have you heard about the Exo Terra's? I've not heard of anything but plenty of good and from what I've seen I want one too.
The primary concerns were poor accessibility to electronics, and the need to remove a million screws - and the cage - to do something simple like adjust gear mesh. If you can look past those things, and get it set up right, they are awesome rigs. And they're cheap now too!
I would ditch the factory motor mount, it is WEAK casted alloy. When I built my kit thats the first bad I had on it. I went with the GCM solid alloy mount and works great. Also the front end is weak in these with the chaeap stamped alloy plates that hold the A-arm pins to the diff case. Smashed my front end within litterally 3 minutes of messin with it in my driveway.
Oh, and the Pro-Line Powerstroke shock kit for the Slash front & rear is what you need if you upgrade, awesome shocks.