Personally, I think when Nirvana was "on" they were amazing. When they weren't, they were pretty average. Overall, I tend to lean more toward the experimental / avantgarde side of music, so I've never listened to the boring crap they churn out for the radio. Frankly, major label (even big independant label) bands have done very little to impress me. Do I greatly enjoy a lot of it? Sure. Impressed? Not generally.

Brad, you especially I think should check out Gridlock. Band is defunct now, but the members still produce music seperately. Their final album "Formless" is especially enjoyable. Challenging at times, but enjoyable.