It's not bad. It's fast, it's easy to use, it returns relavent search results. The interface is a bit busy for my taste, but it's not nearly as distracting as Yahoo. Also, I can't find any official source that says that the name actually stands for "But it's not Google", so I'll let that slide. For now.
If you think of it as a Google-killer, then it's a bit underwhelming. It has not immediate advantages over the beloved G. But if you think of it as a much-needed upgrade to MSN search, then it is a leaps-and-bounds success.
The lesson: don't worry about beating anyone. Just try to be the best you can.