There's absolutely nothing wrong with the Unreal Engine. The misconception that people get is that the engine that a game uses dictates the outcome of the product. It's nothing like that at all, it's merely a starting point that developers customize according to their needs.
If there's a shitty buggy product at the end, the accountability ultimately lands on the developers. Irrational games flaked out with T:V because they made terrible design choices, and didn't focus on the MP aspects. It stood up well as a SP game and that's what they're good at. If you had a company like DICE doing Tribes as an MP focused game, I'm sure the outcome would have been much different.