I don't care about the API at all. I will use it even if it's 10 times harder to use than JNI, as long as it eliminates the performance overhead. We can hide the ugliness in libraries like LWJGL.

My real worries:

1) No matter how good Panama is, there is a strong dependency to Project Valhalla and value types. If that gets delayed (and it very much looks like it will), Panama won't see the light of day, or will have crippled performance. Panama is simple compared to value types. The latter requires serious research and engineering work and there are a lot of open questions. Afaik their priority is on the Java side of things and haven't even touched the fixed/native layout issues yet. Which is expected tbh, there are very few people inside Oracle that actually care about native interop.

2) I doubt we'll be able to use the full power of Panama in user code (custom intrinsics etc). My expectation is that it will be highly restricted for JVM internals (security concerns, Jigsaw bullshit, etc) and we'll again be stuck waiting for Oracle to release the right set of public APIs. What I would prefer instead is that Oracle lays the JVM foundations and the community builds everything else.

3) I'm afraid it's going to be too late for Panama when it is released. Panama, AOT, value types, it will all be great, but when? Even Jigsaw hasn't been released yet (and most people I know hate it already). Meanwhile, projects like Scala Native and Kotlin Native will get the job done.