In addition to VFR nav, I'd add R/T - significant differences to the U.S. and practical weather decision making, particularly if you have conducted your previous flying in a place where the weather is either obviously fine or definitely no go, like FL or AZ, i.e. no marginal or frequently changing conditions.
FAA examiners put complete emphasis on the PTS during the check - any deviation tends to be met with a 'pink slip' whereas EASA examiners are generally allowed more latitude in terms of assessment of the flight which, although comprised of individual sections, is evaluated from the perspective of the whole trip; of course a section can be found to be unsatisfactory but there is a more tempered approach to the appraisal. I find the FAA DE's to be unforgiving of any small oversight - good flight, demonstrating overall good airmanship and performing all manoeuvres satisfactorily but forgetting to hold the checklist and read from it once is likely to result in a fail. I recall a DE I knew telling an unsuccessful candidate that although the flight was good, not knowing the minimum number of static discharge wicks required for a C172 was unfortunately, a fail. The DE added that although he didn't want to have to award the 'pink slip', the Federal Government demanded it
IR training and environment completely different - a lot of emphasis on NDB tracking and holding plus non-precision approaches in weather, meaning that you don't see the runway environment from the IAP. Flight in controlled airspace with airways legs requiring pressure setting changes under formal ATC can make for a steep learning curve.
Instructional standards and style are different - information communicated quite differently whereby the FAA approach seems to be far more about minimal briefings and letting the student have a go from the start, but then not letting them explore more challenging situations (until they meet them again when solo), whereas the European approach is, or should be, more long briefings, pre-flight brief with thorough explanation, demo, follow through then practice - more teaching than just showing.
Ultimately, it's all horses for courses and I'm not suggesting one is better than the other - just different.