Back on topic, I personally also do very much like the Colossus itself, just not how Command used it. And yeah, they didn't expect the Shivans to have Sathanas class warships. I very much remember the tone in Command's voice when the first Sath in the nebula is discovered, and it pretty much said without saying, "OH ****".
If the Shivans didn't have Sathanas class ships, the Colossus would be the best of the best ship around, but FS2 drove home the point that when you are facing up against an enemy that has GOD-KNOWS-WHAT for its technology and you think you have the best crap in your armada don't be surprised if they have something bigger in larger quantities.
As for the usage of the Colossus, you can't fault Command for using it to get the Iceni, nor can you fault them for using it against the Sath. Command had a choice --- they could either let a Sath rampage through their systems with no idea of its intention (at that time they didn't know it was headed for Capella's sun) or deploy their best warship to duel it.
In retrospect, the only stupid thing about it was that Command should have deployed Mjolnirs and HALF THE FLEET against the Sathanas but despite having MANY scans of the Sathanas' specifications decided to pit the Colossus against the Sathanas alone.
The GTVA Colossus is a freaking awesome ship and perhaps the most tragic of any ship in the game. Its destruction was the equivalent of sending the most elite fighter pilots into a suicide mission with no backup --- which quite frankly HAPPENED --- *COUGH* "DIVE DIVE DIVE HIT YOUR BURNERS PILOT" ... I never thought of the Colossus as a failure, I instead always wished that the GTVA would get NEW FRIGGIN FLEET ADMIRALS.