I agree about the Rome car chase - but I wonder whether that was Mendes´ fault.
It could have been the consequence of severe restrictions by the city (wasn´t there some issue with the officials?). It could also have been due to the stunt coordinator´s ideas. It could have been because of budget limitations. And wasn´t this sequence shot after Craig was injured and not available as he should have been? Also, there was heavy rain during the shooting in Rome, right?
I get the feeling that SPECTRE was a very troubled production from the start. Even from preproduction or even before that.
SKYFALL was such a box office behemoth that everybody must have tried to meddle: "This film MUST be as big or even bigger! And don´t change things too much!" - "No, go for more fun! Broader!" - "Do both!"
A typical "damned if you do, damned if you don´t"-situation for everybody, with huge pressure to deliver. I could very well imagine Mendes to curse himself for letting him persuaded to come back because now everybody would measure him based on SPECTRE, not on SKYFALL. After SKYFALL Mendes was the great saviour of the franchise. If he had skipped the next one people probably would say now: Mendes must come back, only he knows how to do it right.
It seems he bit off more than he could chew. He probably thought: Well, I know how to handle this now. It will be easier. And then all the problems showered down on him. Including the SONY leaks, severe budget cuts and Craig´s injury (probably causing a general aversion to Bond at that time). Combined with the problems with John Logan´s work - the writer Mendes had brought in and who seems to have disappointed this time, so much that Mendes reportedly had to beg Purvis & Wade (who did not want to return after SKYFALL, by the way) to step in at the eleventh hour.
I guess that´s why SPECTRE is hit and miss, a patchwork of scenes, some inspired, some tired, some very good, some awfully wasted chances.
Which might entice him, ironically, to come back once more. To prove that SKYFALL was typical for him, not SPECTRE.