One of the many problems with Tilke tracks is the constant pointless jinks and curves here and there. Those that aren't a challenge in
any car, and nowhere is it more in evidence than in Valencia. They're fine if they've got a purpose, such the first part of Blancimont at Spa (where Burti crashed, where they can't change it due to a ravine on the other side, and it used to be @#$%& scary, as well as the 2nd part of Blancimont), or the kink at the bottom of the hill at Istanbul (where they needed it to create a straight without running through the back of the pits). Valencia looks bollocks. It was probably OK in a sketch of idea, before any calculations where done, but that's it. How could it become a race track looking like that? Valencia has about 15 corners in total, and the other 10 are just random kinks.
Another issue is the lack of challenge. They're all billiard-table smooth. Valencia has 2 good corners (at the end) and possibly the double left-hander on full tanks.
Arguably the best new F1 track of recent times has been Singapore. It's bumpy, it's a proper street course, it's got armco right next to the track, and to my knowledge, it's the only one which Tilke didn't design (though apparently he did propose one).
Finally, and I said this in Abu Dhabi last year, yes, slow corners leading on a straight are technically the best when it comes to overtaking, yet in practise that's seldom the way it works. In a corner the driver behind will always be on the throttle more than a car length behind - yet in a slow corner, the time travelled over a car length is greater than say a 2nd or 3rd gear corner (like in Istanbul).