Voted 1 - Initial satisfaction is same level as when I first used my 70-200 mark 2. Both lenses exceeded my personal expectations. Well worth the wait and pre-order "premium price" for me. YMMV
I wish someone would take some identical comparison shots with the new 100-400 and the great 70-200 2.8 ii at the same focal length. Such as 100mm and 200mm. I'm thinking a lot of peeps with the 70-200 would enjoy seeing that. (Or not, if the 100-400 blows it away!)
Have both, but haven't compared them head-to-head. However - keep in mind, between 135-200mm you're at f/5, a full 1 2/3 stops SLOWER than the 70-200 2.8...the difference between ISO 1600 and ISO 5000...
Having used the 70-200 2.8 a lot, though, I know it has excellent performance at 200 - and after test-shooting with the 100-400, it didn't seem to be noticeably better (or worse) to me at 200...
Perhaps this will help, though - a direct comparison at TDP at 200mm, wide open (f/5 vs. f/2.8!!)...seems close to me
200mm, Both at f5.6...can't tell a sharpness difference but the 70-200, being a 2.8 lens, has less corner darkening
I'd say in less than good light, the ISO difference will have a much larger impact on IQ than any perceived optical difference between the two lenses...